bluuebunny/crossref_metadata_2025 huggingface dataset:
Method of superposition applied to axisymmetric structures
Authors: Sarkissian Angie
Published: July 2002

The method of superposition is applied to axisymmetric structures to solve for the scattered field produced by a general, non-axisymmetric incident field. The scattered field is written as a sum over the fields produced by rings of source distributions placed on a surface inside the scatterer. The source distribution on each ring is next expanded in circumferencial modes. Similarly, the field produced by the source distribution is expanded in circumferential modes. The source distribution is solved for by requiring the scattered field to satisfy the proper boundary conditions on the structure surface. This reduces the computational load of the method previously applied of placing point sources on a surface inside the structure since it reduces the size of the matrices to be inverted, thus extending the applicability of the method to higher frequencies. Results are shown for a finite cylindrical structure with hemispherical end-caps satisfying soft boundary conditions. [Work supported by ONR.]
Spectral properies of Christoffel equation for Rayleigh waves
Authors: Kuznetsov Sergey , Kaptsov Alexander
Published: July 2002

Spectral properties of the matrix Christoffel equation are needed for construction of the exponentially decaying surface (Rayleigh) waves. The following analysis covers theorems on root characterization, the structure of eigenvalues, and eigenspaces of the Christoffel equation. The main results are obtained by three-dimensional complex formalism, which goes back to Rayleigh. For the case of anisotropic media this approach was exploited by Farnell in numerical analysis of Rayleigh waves propagating in anisotropic crystals and in analytical study by Stoneley and later by Dieulesaint and Royer. Sextic formalism for Rayleigh wave analysis was proposed by Stroh. This is based on the similarity of solutions for line dislocations in unbounded medium and the propagation of Rayleigh waves. This approach was developed by Barnett and Lothe and later by Chadwick et al., so theorems of uniqueness and existence for Rayleigh waves were proved. Substitution of a complex root in Christoffel’s equation produces an equation for the eigenvector (amplitude vector) determination. Propositions which flow out directly from the analysis of the structure of this equation describe spectral properties and characterization of eigenspaces. One of the most interesting results asserts that algebraic multiplicity of the phase speed equals its geometric multiplicity. [Work was supported by INTAS 96-2003.]
All good oscillations must come to an end
Authors: Moss William C. , Levatin Joanne L. , Szeri Andrew
Published: July 2002

The Rayleigh–Plesset equation (RPE) describes the growth, collapse, and subsequent rebounds of a sonoluminescing bubble, as long as unphysical values of the surface tension and viscosity are used. If realistic values of the surface tension and viscosity are used, the RPE produces insufficiently damped bubble dynamics, which disagree with experimental data. Every derivation of the RPE assumes that the compressibility of the liquid gives rise to the damping. We show that the compressibility of the liquid is at most a second-order effect. The damping comes from the most compressible component of the system, which is the gas, not the liquid. This simple physical reasoning generates a new RPE that reproduces the extreme damping that is observed experimentally, using tabulated values of surface tension and viscosity; a result that is unobtainable with all previous versions of the RPE. Our results affect the calculated limits of stability of sonoluminescing bubbles as well as the calculated magnitude of acoustic emissions from collapsing bubbles. a)This work was performed under the auspices of the U.S. Department of Energy under Contract No. W-7405-Eng-48. b)Supported by NSF.
Circumferential waves on an immersed, fluid filled elastic cylindrical shell
Authors: Bao X. L. , Raju P. K. , Uberall H.
Published: July 2002

The existence of various types of circumferential waves, both predominantly shell or fluid borne, and the repulsion of their dispersion curves is discussed here for an infinite, thin elastic, circular-cylindrical shell immersed in a fluid and filled with another fluid. The study is based on analytic calculation of the partial-wave resonances in the acoustic scattering amplitude of a normally incident plane wave. A large number of cases of repulsion are found in the phase-velocity dispersion curves of the various types of circumferential waves due to the shell-fluid coupling.
The prelexical code hypothesis
Authors: Dupoux Emmanuel , Pallier Christophe
Published: July 2002

The prelexical code hypothesis states that there exists a level intermediate between acoustic/phonetic representation and lexical entries. This level encodes syllable-sized structural aspects of the speech stream in a language-specific fashion. We review evidence in favor of this hypothesis in recent studies using phoneme and fragment detection, adaptation to distorted speech, discrimination, ERPs, long-term priming, as well as studies of speech perception in the young infant. We present evidence that such a prelexical code is compiled during the first years of life and remains unaffected by later linguistic experience. We then discuss the competing hypotheses as to the detailed format of the prelexical code (syllables, half-syllables, autosegmental representations, etc.).
Perceptual adaptation to talker-specific characteristics of speech
Authors: Nygaard Lynne C.
Published: July 2002

Recent research suggests that familiarity with a talker’s voice increases the intelligibility of their speech. Listeners who have learned the specific vocal characteristics of a talker are better able to perceive the linguistic content of that talker’s speech than listeners who have not. Studies will be presented that used a voice learning paradigm to investigate the nature of this perceptual adaptation to talker’s voice. In each study, listeners were familiarized with a set of talker’s voices and then tested on their ability to extract the linguistic content of speech. Two general questions were addressed. First, what type of learning is necessary to become familiar with a talker’s voice? Second, what kind of knowledge is acquired when listeners learn to recognize voices? In general, the results suggest that perceptual adaptation to a talker’s voice is extremely detailed and context-dependent. These findings suggest that any proposed mechanism of perceptual compensation in speech must include long-term memory for specific talker characteristics.
Lexical activation produces impotent phonemic percepts
Authors: McQueen James M. , Cutler Anne , Norris Dennis
Published: July 2002

Dutch listeners categorized a /ta/–/da/ continuum before adaptation, and again during an adaptation phase in which they heard multiple repetitions of five different words. Dutch words, like English words [A. G. Samuel, Cog. Psych. 32, 97–127 (1997)], produced reliable adaptation: there were more /t/ decisions when each adapting word contained a /d/ (and no /t/’s) than when each word contained a /t/ (and no /d/’s). But when these phonemes were replaced with signal-correlated noise, such that the phonemic restoration illusion was induced, there was no adaptation, contrary to the English results. Thus, although listeners heard the replaced phonemes in the noise, these phonemic percepts did not cause adaptation. These results are consistent with the Merge model [Norris et al., Behav. Brain Sci. (in press)], in which the lexicon can influence phonemic decisions (and hence the restoration illusion), but, because there is no feedback from lexical to prelexical levels, cannot induce acoustic-phonetic adaptation. Samuel (1997) claimed on the basis of his results that the lexicon can produce potent phonemic percepts, that is, percepts which can modulate prelexical processing; the present results challenge this claim.
Pressure-particle acceleration underwater acoustic intensity sensor
Authors: Kim Kang , Lauchle Gerald C. , Gabielson Thomas B.
Published: July 2002

An underwater acoustic intensity sensor designed to measure one component of the acoustic intensity vector is discussed and evaluated experimentally. This sensor consists of a pressure transducer in the form of a piezoceramic hollow cylinder, and an accelerometer mounted inside of the cylinder. This is a pressure–acoustic particle acceleration type of intensity probe, and is henceforth denoted as a ‘‘p-u-dot intensity probe.’’ The probe body has syntactic foam endcaps that are adjusted in thickness to allow the entire assembly to be neutrally buoyant. It is coated with polyurethane for waterproofing while maintaining acoustical transparency in water. Each of the two transducers making up the intensity sensor is calibrated individually in both air and water. The integrated intensity probe is calibrated in a water-filled plane-wave tube. It is shown that this neutrally buoyant underwater acoustic p-u-dot probe measures one component of sound intensity that is in very close agreement to the predicted value using slow-waveguide acoustic theory. Some limitations in the experiments and future works are discussed. [Work supported by ONR, Code 321 MURI in Acoustic Transduction: Materials and Devices.]
Modeling the unsteady forces on a finite-length circular cylinder in cross-flow
Authors: Capone Dean E. , Lauchle Gerald C.
Published: July 2002

Semi-empirical models, for unsteady lift, drag, and axial forces, are developed to predict the spectral features of the unsteady forces on a finite-length, right circular cylinder in cross-flow. In general, the models consist of two parts; the spatial variation of rms wall pressure on the cylinder, and the correlation lengths, or areas, which describe the spatial extent of the correlation of the unsteady pressures. Experiments were conducted in a low-noise wind tunnel to measure the statistics of the unsteady wall pressures on a model cylinder. The results from the measurements are incorporated into the theoretical models, and predictions are made for the spectral characteristics of the theoretical lift, drag, and axial forces. The unsteady lift and drag predictions using the models developed in this work agree well with previously measured unsteady force data measured on gradient hyrdophones exposed to flow. Below St=0.8 the unsteady lift and drag are found to be the dominant force on the cylinder, while above St=0.8 the unsteady axial force dominates.
The construction and operation of the khaen
Authors: Miller Terry E.
Published: July 2002

The khaen is perhaps the most important musical instrument of the Lao people of northeastern Thailand and Laos. It is constructed with free reeds mounted in bamboo pipe walls inside a carved wooden wind chamber. Each reed of the khaen sounds for both directions of air flow (inhaling and exhaling). The reed vibration is strongly coupled to the pipe resonance, and the reed will sound only if a small hole near the reed is closed, causing the resonant frequency of the pipe to be near that of the reed. The construction of the khaen is discussed and illustrated with video recordings made in northeastern Thailand. Principles of operation of the instrument are discussed and demonstrated. Comparisons will be made with other Asian free reed instruments.
Measurement of shallow-water reverberation characteristics
Authors: Cable Peter G. , Carey William M.
Published: July 2002

The frequency dependence and level of shallow-water (SW) reverberation, key parameters in sonar performance, represent the combined effect of scattering from the bottom, volume, and sea surface, and are a function of the transmission loss. SW, however, has the attribute of a seasonal dependence to the sound-speed structure, which can emphasize one of the above. A downward refracting profile in a gently sloping environment emphasizes the bottom and when the transmission is measured provides for a means of correcting for this loss and estimating the angle of incidence. This paper describes such measurements performed in several SW–sandy-bottom experiments with horizontal arrays, vertical arrays, and specially designed and calibrated sources. The scattering results are shown to be homogeneous and isotropic and to exhibit a frequency-dependent characteristic below 1 kHz with a minimum value apparently determined by the sediment layering. Numerical modeling suggests that scattering arises from the top several meters of sediment. The values determined here are consistent with previous measurements and the angular dependence determined by the use of vertical arrays and analytical calculations are consistent with Lambert’s Law. Limits on the values of this type of reverberation and performance differences with sonar operating frequency are discussed.
Studies of shallow-water acoustic coherence using the modal phase structure function
Authors: Sperry Brian , Lynch James
Published: July 2002

The modal phase structure function, defined by the cross correlation of the phase for any given mode at two different points in space, time, or frequency, can provide some useful insights into the physics of array coherence in shallow water. Using this indicator of the acoustic field coherence, as well as the usual 〈pp*〉 definition, we examine the coherence of acoustic signals in the 10-to-1000-Hz range scattered by both bottom and water column inhomogeneities. In previous work (Sperry, Ph.D. thesis, 1999), we emphasized large-scale water column inhomogeneities, and ignored some of the finer scale ocean phenomena that could cause significant mode coupling. In this work, we address both phenomena and the general issue of mode coupling. In particular, we address the soliton field in the water column and small-scale inhomogeneities in the bottom sediments. Water column environmental data from the PRIMER experiment and bottom environmental data from the STRATAFORM experiment are used to guide our analyses. Results are compared to acoustic observations for the PRIMER experiment, where both acoustic and environmental data were gathered simultaneously. [Work supported by ONR.]
Studies of internal wave and bottom effects on broadband shallow-water propagation
Authors: Duda Timothy F. , Preisig James C. , Frisk George V.
Published: July 2002

Broadband numerical modeling of acoustic propagation through the continental-shelf environment is used to evaluate the impacts of various natural features on 50–1000 Hz signals. Previous studies have shown that thermocline depth variations due to internal waves, bores, or fronts cause mode coupling. Furthermore, if the coupling causes net flux of acoustic energy into efficiently propagating low-order modes, then more energy propagates to distant ranges, and vice versa. In addition, for moving internal waves the signal changes over time, with time scales of minutes. These effects are dependent on geoacoustic properties of the seafloor and on frequency. Details of the effects are quantified for various depths, bottom types, and frequencies. [Work supported by ONR Ocean Acoustics.]
Acoustic propagation measurements in the surf
Authors: Commander Kerry W. , Stroud John S.
Published: July 2002

As part of the Near Shore Acoustic Network Experiment (NSANE), measurements were conducted in a very shallow water (VSW)/surf zone (SZ) region to investigate acoustic propagation and coherence in coastal areas. These measurements utilized an acoustical array of 16 hydrophones (supplied by Datasonics, Inc.) deployed over many tens of meters, and a broadband source. The data to be presented were acquired from hydrophones on two vertical arrays, separated by 240 m, which comprised half of the total array. The broadband projector was operated in the 3.5–28 kHz range using a variety of pulse types. The projector was aimed seaward, as it was located closer to shore than any of the receivers. Data were acquired in conjunction with environmental data by other NSANE team members. The data were analyzed using coherence techniques. Results of this acoustic measurement will be reported. [Work supported by ONR Code 321OE.]
The acoustic environment of the surf zone
Authors: Deane Grant B. , Stokes M. Dale
Published: July 2002

The topics of this presentation are the factors that determine acoustic transmission and ambient noise in the surf zone. The transmission and reception of acoustic signals in the surf zone are complicated by a rich variety of oceanographical phenomena. The bubble field created by breaking surf strongly absorbs and scatters sound, and the reception of acoustic signals transmitted through the breaking region is quite sensitive to the sizes and spatial distribution of bubbles in both the horizontal and vertical directions. Because wave-induced bubbles are advected by prevailing long-shore and off-shore currents, a deterministic solution to the transmission problem requires a coupled oceanographic/acoustic model, and in addition must include the effects of bubble absorption, surface wave scattering and multi-path propagation in the wedgelike, near-shore waveguide. Temperature gradients caused by shoaling internal waves and bubble-induced sound speed profiles may also play a role in signal transmission. Some examples of these phenomena and their effect on acoustic transmission will be given. Ambient noise, which also forms part of the surf zone acoustic environment, will be discussed; the dominant sources in the surf zone are wave breaking noise, biological sounds and, in populated regions, manmade noise. [Work supported by ONR.]
Planning for the first Asian Sea International Acoustics Experiment (ASIAEX)
Authors: Simmen Jeffrey , Denner Warren W.
Published: July 2002

Organization and planning has been ongoing for the first comprehensive international shallow water acoustic experiment in Asia. Four workshops have been held to reach the final scientific plan: December 1997 (San Francisco), June 1998 (Seattle), April 1999 (Singapore), and July 1999 (Anchorage). This paper will describe ASIAEX, which will consist of two components—volume interaction and bottom interaction. The sites for these components are expected to be a shelf break region in the South China Sea and a shallow water region in the East China Sea, respectively. ASIAEX may involve scientists from the United States, China, Taiwan, South Korea, Singapore, and Russia.
Effects of bathymetry on long-range acoustic transmissions
Authors: Heaney Kevin , Sperry Brian , Tiemann Christoper
Published: July 2002

Long-range acoustic propagation has been used recently to perform basin scale inversions of the temperature field of the oceans. The inversion technique involves measuring acoustic travel times and inverting them for sound-speed structure using a forward acoustics model. Ocean acoustic tomography has generally been formulated and applied to problems with little bottom interaction where ray theory is a suitable forward model. Power and reduced source motion requirements have led the global acoustics community to use near-seafloor moored sources off the coast of islands or continents. We examine the effects that scattering with the seafloor near the source and near the receiver has on broadband acoustic signals. Comparisons are made between range-dependent oases, the parabolic equation, and ray codes for several bottom types and bathymetry contours. The effect of scattering on travel time structure in time/depth space as well as mode amplitudes will be addressed. The implications of this work to future plans for global scale acoustic thermometry and internal wave inversion will be presented.
Large signal dielectric losses in sonar transducers
Authors: Robinson Harold C. , Moffett Mark B.
Published: July 2002

The dielectric loss factor tanδ is a critical parameter in transducer design and performance prediction, as it is directly related to the electrical energy lost to Joule heating. For an ideal linear material, tanδ is a constant irrespective of the operating conditions. However, electrostrictive materials such as lead magnesium niobate/lead titanate (PMN/PT) exhibit significantly nonlinear behavior. It is, therefore, expected that tanδ (as well as the other material constants) will be a strong function of the transducer operating conditions. In this paper we will present three different methods for calculating the loss factor of ‘‘quasilinear’’ materials. It will be shown that, in the limit of small signals about a bias point, the three methods are consistent with the standard linear definition. These three methods will be applied to material measurements taken at NAVSEA Newport on PMN/PT. The behavior of the loss tangent as a function of the dc bias field, ac drive field, prestress level, and temperature will be examined. Finally, the predicted response of stacks and transducers using tanδ calculated from the material measurements will be compared with experimental results. [Work sponsored by PEO(USW)-P and the Office of Naval Research.]
A review of acoustic localized wave phenomenology
Authors: Ziolkowski Richard W.
Published: July 2002

A brief review of the history that led to several classes of exact solutions of scalar wave equations that describe localized transmission of acoustic wave energy will be given. It has been shown that these acoustic localized wave (LW) solutions can be optimized so that they are localized near the direction of propagation and their original amplitude is recovered out to extremely large distances from their initial location. Pulses with these very desirable localized transmission characteristics have a number of potential applications in the areas of directed energy systems, secure communications, and remote sensing. Simulations will be shown for several aspects of LW pulse-driven arrays. Various performance criteria including near-field and far-field sidelobe, intensity, and energy distributions will also be discussed for acoustic LW pulse-driven arrays. Since these LW arrays deal with different ultra-wide bandwidth driving pulses at each element of the array, these criteria are generalizations of the standard continuous wave (CW), phased array results. Recent attempts to reduce the equivalent sidelobe levels will also be discussed. Past acoustic experimental setups and results will be summarized briefly in regards to all of these time domain versus frequency issues.
Stochastic matched field processing
Authors: Baggeroer Arthur B. , Scheer Edward K.
Published: July 2002

Stochastic matched field processing was introduced [Baggeroer and Kuperman, J. Acoust. Soc. Am. 91] as a means to address stochastic variability and signal gain degradation in a replica signal. The approach parallels what is usually termed the ‘‘random signal in noise’’ problem in time series analysis wherein one uses a stochastic model to respond to the signal gain degradation issue when high-fidelity replicas cannot be generated. For stochastic MFP the important issues are: (i) the signal power scatters into a ‘‘red’’ spectra of eigenvalues where only a small number are significant, (ii) the eigenvectors are predictable based upon a priori environmental data such as internal wave or signal motion models in addition to nominal sound speed models. For many environments these conditions are met and, and importantly, more robust, MFP can be obtained. This presentation will review (i) stochastic matched field, (ii) apply it to deep and shallow water random ocean models, and (iii) assess its performance using Chernoff detection theory bounds for low signal-to-noise ratio scenarios.
Non-Gaussian randomness outside and inside the bat’s brain
Authors: Müller Rolf , Kuc Roman
Published: July 2002

Reflector placement in the habitats of bats is pronouncedly random. Furthermore, the impulsive nature of reflection sequences generated by facets found, e.g., in foliage can endow the probability density function of the received echo amplitudes with heavy tails. Two useful features for classification of foliages, which may be utilized by bats as ubiquitous landmarks, are the extent to which the amplitude distribution deviates from Gaussian (its ‘‘peakiness’’) and an eventual nonstationary gain of the propagation channel. The signal processing in the bat’s auditory system does not have direct access to the target’s reflection sequence, however. Even the shortest echolocation pulses seen in bats are chirps with durations, which are nonnegligible compared to the duration of the reflection sequence and the temporal spacing of salient peaks inside of it. On reception, echoes are subjected to bandpass filtering and demodulation. The latter step prohibits recovery of the reflection sequence by means of pulse compression using a matched filter. Consequently, it is investigated how the demodulated filter bank output may be used directly as a substrate for target classification. Specifically, the possible role of encoding the waveforms in sparse spike trains and comparing binaural information is evaluated.
Frame bulk and shear moduli of air and water saturated glass beads
Authors: Kimura Masao
Published: July 2002

Are the values of the frame bulk and shear moduli of air saturated sediments, and those of water saturated sediments, the same or not the same? This problem is currently under debate. In this study, the frame bulk and shear moduli of air and water saturated glass beads with five different grain sizes are derived from the measured values of the longitudinal and shear wave velocities in these media. The grain sizes are 0.05, 0.1, 0.2, 0.4 and 0.8 mm. The longitudinal wave velocities are measured using piezoelectirc transducers with the operating frequency of 11.8 kHz for dry sample, and 500 kHz for wet sample. The shear wave velocities are measured using bimorph type piezoelectric transducers with the operating frequency of 3.5 kHz for both samples. The relationship between the values of these moduli in air and water saturated glass beads and the effect of grain size are investigated.
Geoacoustic inversions in a very shallow water environment
Authors: McArthur K. M. , Hodgkiss W. S.
Published: July 2002

The genetic algorithm is used to invert the geoacoustic parameters of a near shore, very shallow water region (from 10-m to 20-m water depth). The experimental data are source tows in the frequency range from 70 Hz to 700 Hz recorded on a horizontal line array of a 120-m aperture. The source tows were conducted offshore of Camp Pendleton, north of Oceanside, CA, along range-independent and range-dependent bathymetry tracks. Generally, a thin layer of sediment overlies a harder subbottom in this region. An echosounding survey, a sediment coring survey, and regional geologic information are used to develop background geoacoustic models. Inversion results from transmission loss versus range data agree well with the results obtained from inverting complex-pressure data across the array for a single range.
Improved signal processing techniques for measurement of the inter-pulse interval (IPI) of sperm whale clicks
Authors: Hayward Thomas J. , Pavan G.
Published: July 2002

Improved signal processing techniques are described for estimating the inter-pulse interval (IPI) associated with the multiple pulses in a sperm whale click. These pulses are believed to result from repeated reflections of the original pulse within the spermaceti organ in the whale’s head. Previous estimates of the IPI have been based on time series correlation or on computation of the cepstrum of the received waveform [J. Goold, J. Acoust. Soc. Am. 100, 3431–3441 (1997)]. The present work describes real-time computation and display of the spectrogram and cepstrogram (time-cepstral distribution) [G. Pavan, Proc. IoA 19 (1997)] and examines the benefits of the simultaneous display of this information for field analysis and for browsing long recordings to identify sperm whale clicks. In addition, a detailed model of the spectral modulation associated with the multiple pulses is developed and leads to improved estimation of the IPI. Examples are presented that indicate the method may be more robust with respect to additive noise and the effects of surface reflection than the cepstrum-based approaches. [Work of the first author supported by ONR. Work of the second author supported by the University of Pavia, Italy, the Italian Ministry of the Environment, and by the Italian Navy.]
Geoacoustic and signal gain modeling in a range-dependent, shallow-water environment
Authors: Rozenfeld Ilya , Carey William M. , Cable Peter G. , Siegmann William L.
Published: July 2002

The Acoustic Characterization Test III (ACTIII) was conducted in the Strait of Korea in 1995. One of the goals of the experiment was to determine limitations on spatial signal processing due to environmental variabilities. Measurements of transmission loss and array signal gain (ASG) provide quantitative estimates of fluctuations in the acoustic field. Analysis of observations is supported by using grab samples, historical cores, and seismic measurements to develop a geoacoustic model. The geoacoustic model along with sampled bathymetry and sound-speed profiles is used to generate simulations of an effective attenuation coefficient, which measures the rate of change of mean transmission loss with range. The introduction of nonlinear frequency dependence into sediment attenuation profiles produces good agreement between the simulations and measured data. The ASG is directly related to the spatial coherence function. By employing procedures we have developed previously for approximating the coherence function, we use the environmental model to compute ASG. This allows further comparisons with experimental data as well as a determination of validity limits for the procedures. [Work supported by ONR.]
Free-field audiogram of the Japanese macaque (Macaca fuscata)
Authors: Jackson Laura L. , Heffner Rickye S. , Heffner Henry E.
Published: July 2002

The audiograms of three Japanese macaques and seven humans were determined in a free-field environment using loudspeakers. The monkeys and humans were tested using tones ranging from 8 Hz to 40 kHz and 4 Hz to 22.4 kHz, respectively. At a level of 60 dB sound pressure level the monkeys were able to hear tones extending from 28 Hz to 37 kHz with their best sensitivity of 1 dB occurring at 4 kHz. The human 60-dB hearing range extended from 31 Hz to 17.6 kHz with a best sensitivity of −10 dB at 2 and 4 kHz. These results indicate that the Japanese macaque has low-frequency hearing equal to that of humans and better than that indicated by previous audiograms obtained using headphones.
Training American listeners to perceive Mandarin tones
Authors: Wang Yue , Spence Michelle M. , Jongman Allard , Sereno Joan A.
Published: July 2002

Auditory training has been shown to be effective in the identification of non-native segmental distinctions. In this study, it was investigated whether such training is applicable to the acquisition of non-native suprasegmental contrasts, i.e., Mandarin tones. Using the high-variability paradigm, eight American learners of Mandarin were trained in eight sessions during the course of two weeks to identify the four tones in natural words produced by native Mandarin talkers. The trainees’ identification accuracy revealed an average 21% increase from the pretest to the post-test, and the improvement gained in training was generalized to new stimuli (18% increase) and to new talkers and stimuli (25% increase). Moreover, the six-month retention test showed that the improvement was retained long after training by an average 21% increase from the pretest. The results are discussed in terms of non-native suprasegmental perceptual modification, and the analogies between L2 acquisition processes at the segmental and suprasegmental levels.
Vestibular responses to loud dance music: A physiological basis of the “rock and roll threshold”?
Authors: Todd Neil P. McAngus , Cody Frederick W.
Published: July 2002

In this paper new evidence is provided to indicate that vestibular responses may be obtained from loud dance music for intensities above 90 dB(A) SPL (Impulse-weighted). In a sample of ten subjects acoustically evoked EMG were obtained from the sternocleidomastoid muscle in response to a sample of techno music typical of that which may be experienced in a dance club. Previous research has shown that this response is vestibularly mediated since it can be obtained in subjects with loss of cochlear function, but is absent in subjects with loss of vestibular function (Colebatch et al. [J. Neurol. Neurosurg. Psychiatr. 57, 190–197 (1994)]. Given that pleasurable sensations of self-motion are widely sought after by more normal means of vestibular stimulation, it is suggested that acoustically evoked sensations of self-motion may account for the compulsion to exposure to loud music. Given further the similarity between the thresholds found, and the intensities and frequency distributions that are typical in rock concerts and dance clubs, it is also suggested that this response may be a physiological basis for the minimum loudness necessary for rock and dance music to work—the “rock and roll threshold” [Dibble, J. Audio Eng. Soc. 43(4), 251–266 (1995)].
Wave-number-based assessment of the doubly asymptotic approximation. II. Frequency and time domain response
Authors: Ginsberg Jerry H.
Published: July 2002

In part I, the surface variational principle (SVP) and the doubly asymptotic approximation (DAA) were used to generate alternative descriptions of the frequency domain wet surface impedance. These are used here to obtain alternative descriptions of the displacement field in slender hemicapped cylindrical shells. This field is represented as a decomposition into a two-dimensional wave-number space. The responses that are obtained are frequency domain transfer functions for a point force at the midplane, evaluated for a discrete set of frequencies. Solutions obtained from first- and second-order versions of DAA are compared to the SVP result. Then temporal responses are obtained by using an inverse fast Fourier transform to evaluate the convolution of the transfer functions with a prototypical temporal excitation. The results reveal that DAA and SVP differ most in the vicinity of fluid-loaded resonances. The largest disagreement is encountered for the axisymmetric portion of the response. It is shown that DAA often greatly underpredicts peak displacements and accelerations, but a few cases lead to overprediction.
Interaction between wave number pairs for a capped cylinder
Authors: Ille J-F. , Ginsberg J. H.
Published: July 2002

When acoustic-structure interaction is analyzed according to the wave number-based version of the surface variational principle (SVP), considerable computational effort is required to generate each coefficient in the quadratic sum forming the variational quantity. Examination of the wet-surface impedance, which represents the spectrum of pressure amplitudes generated by a specified spectrum of surface velocity amplitudes, reveals that many cross-impedance terms are very small. This suggests that some coefficients need not be computed. The article introduces a priori criteria for selecting the impedance terms to be omitted, based on the supersonic cutoff wave number. Each truncation scheme is assessed by comparing its predictions to the convergent SVP solution. It is shown that, for the nonsymmetric azimuthal harmonics, the field quantities and the radiated power are well predicted if subsonic waves are ignored. In contrast, for the axisymmetric component, substantial errors (6 dB or more) for radiated power arise, unless a broad spectrum of subsonic waves are included in the formulation. The complex power is mostly reactive, being associated with an evanescent field, even for the supersonic spectrum. The study shows that small interactions between subsonic waves in the axisymmetric case can result in the high wave number spectrum being associated with substantial radiation contributions.
Wideband determination of source functions using the Faran elastic sphere scattering model
Authors: Feuillade C. , Meredith R. W. , Chotiros N. P. , Clay C. S.
Published: July 2002

During August 1998, a bottom scattering tank experiment was performed at ARL-UT to measure wideband reverberation from multiple objects (e.g., cobbles and pebbles) placed on a sediment simulation of the sea floor. As a first step in this experiment, a procedure was adopted to calibrate the source transfer function by measuring reflected signal pings from the water surface (which has a spike impulse response), with the transducer directed vertically upwards. Subsequent analysis showed that the strength of the reflections may have induced a nonlinear receiver response in the transducer. Fortunately, time-domain scattering measurements had also been made with a stainless steel ball suspended in the water column. These data were used to study the source drive by deconvolving the theoretical impulse response of a steel sphere, obtained via the Faran scattering model, from the scattered time signals. Both the characteristics of the experimental source signal and another, low-power, source measured later were examined. Results show the critical importance of accurate input–output system calibrations for wide signal bandwidth sound scattering research, and have implications for boundary and volume scattering applications. Experimental data and theoretical numerical analysis will be presented. [Work supported by ONR.]
A fast method for deducing ground-impedance parameters from measurements of excess attenuation spectra
Authors: Taherzadeh Shahram
Published: July 2002

An efficient numerical method for indirect deduction of ground-surface impedance [J. Acoust. Soc. Am. 105, 2039–2042 (1999)] is used to deduce surface impedance of absorbing grounds and to obtain estimates for the effective flow resistivity of the ground. One-parameter and two-parameter impedance models are used for the parameter-fitting purposes. It is shown that the two-parameter model can be modified to give a better agreement with the measured data at grazing angles
Is hearing all cochlear (revisited)? Frequency tuning and intensity thresholds in acoustically stimulated, myogenic vestibular-evoked potentials (MVEP)
Authors: McAngus Todd Neil P. , Cody Fred W. , Banks Jon
Published: July 2002

There has amassed considerable evidence that the sacculus, an organ of hearing in lower vertebrates, has retained some acoustic sensitivity throughout phylogeny. In humans, myogenic vestibular-evoked potentials (MVEPs) may be obtained from motorneurones inervated by the vestibulo-spinal tract, particularly from the cervical region of the spinal cord. The MVEP has been studied principally as a noninvasive clinical tool for evaluation of normal otolith vestibular function, since traditional nystagmographic methods only really assess canal function. However, we have been interested in what ‘‘auditory’’ function acoustic sensitivity sacculus may have in the perception of sound. The results of a series of experiments are reported which may be summarized as follows. (1) MVEP has a frequency tuning [Todd, Cody, and Banks, Hear. Res. (in press)], with a maximum response frequency between 300 and 350 Hz and a band-width of about 3 octaves. (2) MVEP can be obtained to natural acoustic stimuli [Todd and Cody, J. Acoust. Soc. Am. 107, 496–500 (2000)], such as dance music, above about 90 dB SPL. (3) MVEP can be obtained to continuous sounds. Given the above then, there are a number of possibilities where acoustic sensitivity of the sacculus may play a role in human perception.
Robust speech localization using formant phase subtraction
Authors: Aarabi Parham , Pratt Vaughan
Published: July 2002

This paper examines the benefits of a context aware time difference of an arrival-based speech localization system. This approach uses information about the formant structure of the speaker in order to compute a more robust time difference of arrival between two microphones. This ability allows microphone arrays to localize speech in environments with signal-to-noise ratios as low as −10 dB, when the noise source is another speaker, and −4 dB, when the noise source is white Gaussian.
Adaptive and synthetic aperture processing structures for high-resolution mine-hunting sonars deploying planar or cylindrical arrays
Authors: Stergiopoulos Stergios , Dhanantwari Amar
Published: July 2002

The developments reported in this paper have been devoted to minimizing the influence of partially directional noise fields as well as maximizing the array gain of mine-hunting sonar systems by means of signal processing. The effort of this study included the design of a generic beamforming structure that allows the implementation of nonconventional signal-processing techniques in integrated active/passive sonar systems. The nonconventional processing schemes of this study are adaptive and synthetic aperture beamformers that have been shown experimentally to provide improvements in array gain for signals embedded in partially correlated noise fields. The reported results show that synthetic aperture and adaptive processing schemes with near-instantaneous convergence can be implemented in mine-hunting sonars deploying 3D arrays. Moreover, practically realizable angular resolution improvements provided by the nonconventional beamformers are equivalent with those provided by the conventional beamformer of a three-times-longer physical aperture and for broadband FM type of signals. The same set of results demonstrates also that the combined implementation of a synthetic aperture and the subperture STMV adaptive scheme suppresses significantly the sidelobe structure of cw pulses for mine-hunting operations. In summary, the present paper attempts to address characterization of source signals detected by planar or cylindrical arrays of mine-hunting sonar systems with 3D image resolution capabilities.
Selective attention to the parameters of a physically informed sonic model
Authors: Lakatos Stephen , Cook Perry C. , Scavone Gary P.
Published: July 2002

Two experiments tested listeners’ ability to attend selectively to the properties of a physical model comprising collisions between multiple independent sound-producing objects. A probe signal paradigm measured attention to two properties—resonant frequency and number of colliding objects. Listeners completed a baseline task measuring absolute sensitivity at each stimulus against a background noise. Subsequently, stimuli served as both cues and targets; cue validity was probabilistic. When cue and target were generated by the same object (Experiment 1), greater detectability occurred with valid cues for both resonant frequency and object number, implying the presence of attentional mechanisms for these properties. When cue and target were generated by different objects (Experiment 2), selective attention persisted for object number but not for resonant frequency.
Human capabilities of dereverberation
Authors: Libbey Brad W. , Rogers Peter H.
Published: July 2002

Humans listening to speech in a small room are frequently unaware of reverberation. It is unknown if neurological processes remove these echoes or if they are simply disregarded when speech is phonetically processed. In other words, is there a neurological mechanism that is capable of removing echoes to create a clean speech neurological signal before phonetic processing? Or is the brain capable of processing reverberant phonemes? Word intelligibility experiments examine these questions. Preliminary experiments investigate how characteristics of simulated reverberation such as room size, absorption of walls, source location, and listener position affect intelligibility. The results of these experiments are used in the design of primary experiments that address human capabilities. In the capability tests the effects of binaural listening, reverberation level, and deconvolution processing are investigated. These experiments approach the fundamental questions through the use of a three-factor experiment (the factors being binaural versus diotic, high versus low levels of reverberation, and simulated reverberation versus convolutional noise). Through the primary and interaction effects of these factors the data illustrates the extent of neurological dereverberation.
Application of reduced-order models to the design of adaptive aeroelastic structures
Authors: Clark Robert L. , Rule John A. , Richard Robert E.
Published: July 2002

Reduced-order models of potential-flow aerodynamics have been developed and greatly facilitate the analysis and design of aeroelastic systems in the early design phase. Models capturing 95% of the physics with 5% of the modeling effort can be realized to evaluate various active and passive design considerations. A delta wing model has been developed to determine the most effective locations for transducers required to provide gust alleviation and flutter control. The basic design philosophy will be presented, and both analytical and experimental results will be discussed. Results from this study indicate that a single sensor/actuator pair can be designed to significantly extend the flutter boundary.
Compliant-backplate Helmholtz resonators
Authors: Horowitz Stephen B. , Nishida Toshikazu , Cattafesta Lou N. , Sheplak Mark
Published: July 2002

The results of a theoretical and experimental investigation into compliant-backplate Helmholtz resonators are presented. The motivation for this study is to develop a prototype energy-reclamation module based upon a Helmholtz resonator that uses a compliant piezoelectric backplate. To establish a baseline case, rigid backplate Helmholtz resonators are first designed using a lumped element model and then tested in a plane-wave tube. The plane-wave tube, in the Interdisciplinary Microsystems Lab at the University of Florida, permits characterization in a known acoustic field at frequencies up to 20 kHz. After this initial testing, the rigid backplate of the resonator is then replaced by a compliant piezoelectric diaphragm and tested in the plane-wave tube. The experimental results are compared to theory based on lumped element modeling of the Helmholtz resonator with a compliant diaphragm. The compliant-backplate configuration results in a lower resonant frequency relative to the rigid-backplate configuration. Finally, the potential for extracting useful energy from broadband pressure fluctuations outside the resonator (e.g., from a grazing turbulent boundary layer) and converting this energy to its electrical form via electromechanical transduction is evaluated. [Work funded by NASA Langley Research Center.]
An experimental and numerical investigation of sound produced by low-speed flow over a cavity with a leading edge overhang
Authors: Henderson Brenda S. , Navaz Homayun K. , Berg Raymond
Published: July 2002

An experimental and numerical investigation is conducted on low-speed flow over a cavity. The production of discrete tones and development of complex flow structures are studied for deep cavities with leading edge overhangs. Experimental results indicate that multiple discrete frequency tones are produced simultaneously or intermittently. The frequency characteristics and maximum sound pressure level depend on the leading edge overhang geometry. The onset of instability and production of multiple tones appear to be affected by boundary layer thickness. Numerical studies show a complex periodic vortex structure in the cavity mouth region, with a period equal to that measured for the dominant tone in the experiments. The vortex structure is affected by the leading edge overhang geometry. Mass addition and extraction from the cavity appear to be controlled by the vortex structure in the cavity mouth, which may explain the effect of lip geometry on peak sound pressure levels in the cavity.