bluuebunny/crossref_metadata_2025 huggingface dataset:
Declination of fundamental frequency in speakers’ production of parenthetical and main clauses
Authors: Kutik Elanah J. , Cooper William E. , Boyce Suzanne
Published: October 2005

An experimental study was conducted to investigate fundamental frequency ( F0) contours in sentences with and without parenthetical clauses. Sentences consisted of a systematically lengthened parenthetical clause inserted between the subject noun phrase and the verb phrase of the main clause. The middle portion of the parenthetical was lengthened incrementally in each sentence to test the effects of sentence length on fundamental frequency contours of seven test sentences. Computer-aided measurements were made for: F0 peaks of key stressed segments; duration of the main clause, parenthetical clause, and clause-final syllables within each; and pauses immediately preceding and following the parenthetical. Mean results demonstrate: (1) a drop in F0 for the parenthetical clause, well below the main clause declination and forming a separate contour of declination; (2) a sharp rise in F0 on return to the main clause; (3) no effect of longer parenthetical length on final segment durations of either the parenthetical or the main clause; and (4) no effect of increased parenthetical length on main clause duration or pause length. These results suggest that parenthetical clauses are mentally programmed as independent constituents, but are subject to some of the same general declination constraints as main clauses.
Further evidence of acoustic invariance in speech production: The stop–glide contrast
Authors: Mack Molly , Blumstein Sheila E.
Published: October 2005

We have conducted a detailed comparative acoustic analysis of the labial stop and glide, [ b] and [w], and we have attempted to identify an invariant acoustic property which can accurately distinguish stops and glides. To this end, we conducted three experiments. In experiment I, we undertook computer analysis of the labial stop [b] and the labial glide [w] as produced in five vowel contexts by two speakers. Results indicated that transition durations and formant frequencies often differed considerably in these two classes of sounds—and to a much greater extent than suggested in previous perception experiments. In experiment II we examined a measure of amplitude—unit energy. We calculated the degree of relative amplitude change occurring in the vicinity of the stop and glide release and found reliably larger changes in energy associated with the stop release than the glide release across vowel contexts and speakers. These changes seemed to provide an invariant property characterizing the stop–glide contrast. In experiment III we tested the generality of our claims by examining a new set of data consisting of the stops [d] and [g] and the glide [y]. Results of this experiment further supported our hypothesis. We have related our findings to a general theory of acoustic invariance in speech.
Vibrotactile identification of vowels
Authors: Green Barry G. , Craig James C. , Wilson Amy M. , Pisoni David B. , Rhodes Roger P.
Published: October 2005

The ability of subjects to identify vowels in vibrotactile transformations of consonant–vowel syllables was measured for two types of displays: a spectral display (frequency by intensity), and a vocal tract area function display (vocal tract location by cross-sectional area). Both displays were presented to the fingertip via the tactile display of the Optacon transducer. In the first experiments the spectral display was effective for identifying vowels in /b\V/ context when as many as 24 or as few as eight spectral channels were presented to the skin. However, performance fell when the 12- and 8-channel displays were reduced in size to occupy 1/2 or 1/3 of the 24-row tactile matrix. The effect of reducing the size of the display was greater when the spectrum was represented as a solid histogram (‘‘filled’’ patterns) than when it was represented as a simple spectral contour (‘‘unfilled’’ patterns). Spatial masking within the filled pattern was postulated as the cause for this decline in performance. Another experiment measured the utility of the spectral display when the syllables were produced by multiple speakers. The resulting increase in response confusions was primarily attributable to variations in the tactile patterns caused by differences in vocal tract resonances among the speakers. The final experiment found an area function display to be inferior to the spectral display for identification of vowels. The results demonstrate that a two-dimensional spectral display is worthy of further development as a basic vibrotactile display for speech.
Measurement of vibration velocity distributions and mode analysis in thick disks of Pb (Zr⋅Ti)O3
Authors: Ueha Sadayuki , Sakuma Sadaomi , Mori Eiji
Published: October 2005

The vertical vibration velocity distributions and the frequency spectra of disk-type transducers with bevelled and unbevelled edges are measured as a function of the diameter-to-thickness ratio. In this experiment transducers of Pb(Zr⋅Ti)O3 are used and the diameter-to-thickness ratios are changed from 2 to 12. The frequency spectra are measured in the band from 1–700 kHz, and the velocity distributions are measured along the radial direction with an optical heterodyne technique. The theoretical frequency spectra are analytically derived from the wave equation of the disk-type transducer and compared to the experimental results. The theoretical velocity distributions are also proven to be true and to agree with the measured ones.
Pressure and pressure gradient fiber-optic lever hydrophones
Authors: Cuomo Frank W.
Published: October 2005

Fiber-optic levers have been found useful in the design of intracardiac pressure transducers, low-displacement biological measurements, and more generally as noncontact optical proximity detectors. In this paper the utilization of a bifurcated fiber-optical lever in the design of hydrophones of the pressure and pressure gradient types has been considered. This approach leads to simplicity, low cost, and relative ease in implementation. Some optical and acoustical considerations are given to establish the validity of the experimental data presented. It is shown that with little effort these devices can provide acoustic sensitivities at least equivalent to those of piezoceramic elements within the same frequency range and can generate acceptable directivity patterns in the pressure and pressure gradient modes.
A series expansion of the acoustic power radiated from planar sources
Authors: Williams Earl G.
Published: October 2005

A series expansion in ascending powers of the wavenumber k is derived for the acoustic power delivered by baffled or unbaffled planar sources. This series provides a relatively simple means of deriving expressions for the power radiated by a baffled source with a known velocity distribution and can be used for unbaffled plates when the velocity field outside the plate is also known. The terms in the series are calculated from the moments of this velocity distribution in the plane containing the source. If these moments are written as derivatives in wavenumber space, it is shown that a MacLaurin expansion of the Fourier transformed velocity provides an easy technique for computing the first few terms of the acoustic power. Examples are provided for baffled, rectangular plates with various boundary conditions. The arbitrarily shaped plate with free boundaries is particularly interesting. It is proven that the volume flow across its surface must be zero and as a result corner and edge mode radiation cannot exist for this kind of source.
Theoretical investigation of the response of gas-filled micropores and cavitation nuclei to ultrasound
Authors: Miller Douglas L. , Nyborg Wesley L.
Published: October 2005

Theory is discussed for the transverse oscillation of a small circular interface set into a rigid baffle between gas and liquid. The angular resonance frequency is given by (15πT/4ρa3)1/2, in which a is the radius of the interface, T is the interfacial surface tension, and ρ is the density of the liquid. Damping parameters are obtained for the radiation, viscous, and boundary-layer mechanisms of dissipation. This model system is extended for discussion of the pulsation of gas trapped in a pit or cavity in a solid, which may simulate one type of cavitation nucleus, and straight-through cylindrical holes or pores in a solid sheet, which is applicable to the hydrophobic membranes with gas-trapping micropores used in studies of biological effects produced by ultrasound. Fixed and free conditions at the three-phase line at the periphery of an interface are considered. Finally, the partially gas-filled cavity is treated, and also the partially gas-filled pore with two interfaces which have different mass, stiffness, and damping parameters. The results of these theoretical considerations are expected to be of value for quantitatively evaluating that specific form of stable cavitation which involves the direct activation of pre-existing, stable bodies of gas into ultrasonic pulsation, as experimentally observed, for example, by D. Miller, J. Acoust. Soc. Am. 71, 471–476 (1982).
Acoustic propagation in the ocean with a poro-elastic bottom
Authors: Yamamoto Tokuo
Published: October 2005

The acoustic normal modes in a homogeneous ocean overlying a homogeneous porous elastic bottom half-space are obtained in closed form. The Biot theory is used to model the bottom. The effects of sediment properties on the dispersion and attenuation of acoustic waves are examined numerically. It is found that the shear modulus and the poro-viscous-frequency number ksf/βν are the two most critical bottom parameters for acoustic attenuation. Here, ks is permeability, f is frequency, β is porosity, and ν is the kinematic viscosity. For sediment and rocks having shear modulus larger than 5×107 N/m2, the shear waves and the slow compressional waves become important in acoustic propagation. For hard porous rocks, such as sandstones and corals, the attenuation of acoustic waves by a porous rock increases with frequency. For a given soft sediment, the acoustic wave attenuation decreases with frequency. For a given frequency, the acoustic attenuation becomes maximum when the sediment properties are such that ksf/βν is about 0.1. Near the critical value ksf/βν=0.1 the energy loss is totally due to the fast compressional waves and the fluid bottom model may be used. However, as ksf/βν deviates from 0.1, the error associated with the fluid bottom approximation increases progressively and becomes unacceptable even for soft sediments.
Modeling ocean-bottom reflection loss measurements with the plane-wave reflection coefficient
Authors: Chapman N. Ross
Published: October 2005

Ocean-bottom reflection loss has been measured at an abyssal plain site in the northeast Pacific Ocean. The layer of unconsolidated sediment at this site is thin (less than 200 m), and the near-surface sediments are composed of strongly reflecting sandy turbidites. In consequence, the surficial sediments and the relatively shallow substrate must be accounted for in describing the bottom loss measurements. The bottom loss has been modeled in this paper using the plane-wave reflection coefficient calculated for a geoacoustic model of the bottom developed from seismic profiling experiments carried out at the site. In the model the sediment column is described by fluid layers with a relatively small value of attenuation and a large value of sound-speed gradient in the surficial layer, and the substrate is assumed to be a solid. The bottom loss measurements are presented in 1/3 octave bands at 40, 80, and 160 Hz. The results are well-modeled at small grazing angles (θ≤20°) where the interaction is confined to the surficial sediments. At larger grazing angles the importance of including a solid substrate is demonstrated.
An ultrasonic bridge for the study of viscoelastic properties of thin interface films
Authors: Rokhlin S. I.
Published: October 2005

The method of elastic interface waves which is currently under development has proven effective in the investigation of viscoelastic properties of interfaces in solid bodies. The present paper is concerned with the development of a modified method of measurement, employing ultrasonic interface waves, which makes it possible to investigate the thermomechanical properties of thin interface layers. The effect of temperature variations in the substrates and transducers is eliminated by using a differential acoustic system. Comb transducers are used for excitation and reception of ultrasonic waves.
A history of violin research
Authors: Hutchins Carleen M.
Published: October 2005

From the probable origins of the violin in the early 16th century there is a long history of experimentation; first, the empirical development of the violin by the makers themselves over more than 200 years to its height of excellence in the late 17th and 18th centuries; then the scientific investigations of its vibrational characteristics which have been done since the early 19th century. These have progressed in spurts of activity associated with technological innovations, particularly the developments of increasingly sensitive measuring equipment. This paper attempts to cover briefly the work of the early mathematicians as well as that of Savart, Helmholtz, and Rayleigh as related to the violin; then considers the research of the 20th century from the pre-electronic investigations of Raman, Miller, and Fuhr, through the spate of activity in violin research from 1930 to 1960 particularly in Germany, the USA, and Japan; and finally a brief overview of the many current developments associated with today’s electronic and optical technologies, along with the concept of the violin as a musical instrument involving research in fields as widely separated as psychoacoustics, musical composition and performance, materials research, vibration analysis, and violin making.
Scattering of elastic waves by a fluid inclusion
Authors: Peterson B. , Varadan V. K. , Varadan V. V.
Published: October 2005

The scattering of harmonic elastic waves by a bounded fluid inclusion in an infinite elastic continuum is considered. The formalism is an extension of the T-matrix method developed for solid inclusions and cavities in elastic media and elastic solid inclusions in fluid media. The problem that is considered here is somewhat more complicated and shares some similarities with the case of an elastic cavity. For the fluid inclusion, however, the scattering amplitudes display resonance peaks due to interior resonances of the fluid. The convergence of the truncated series is dependent on the largest wavenumber which in the cases studied here is that in the fluid inclusion. Numerical results are presented for a prolate spheroidal inclusion.
Finite element eigenfunction method (FEEM) for elastic (SH) wave scattering
Authors: Su J. H. , Varadan V. V. , Varadan V. K.
Published: October 2005

A finite element eigenfunction method (FEEM) is presented for elastic (SH) wave scattering by cylinders of arbitrary cross section. The problem has been analyzed by enclosing the scatterer within an imaginary circular cylinder. The scattered field outside the circular cylinder is expanded in the usual cylindrical harmonics. The nearfield solution inside the circular cylinder is also assumed to be expanded by a series of eigenfunctions. The eigenfunctions for the nearfield are generated through the standard finite element technique by imposing suitable conditions on the circle. Then both the coefficients of the scattered field and those of the nearfield are found by means of a least-square fit for the continuity conditions across the circle. The solution obtained thereby is considered complete in the sense that both the scattered and the nearfields are solved simultaneously. The validity of this method has been verified by comparing results with calculations from exact analysis and the T-matrix method for (a) centered circular cylinder, (b) off-centered circular cylinder, (c) elliptical cylinder, and (d) square cylinder.
A possible auditory basis for internal structure of phonetic categories
Authors: Miller Joanne L. , Connine Cynthia M. , Schermer Trude M. , Kluender Keith R.
Published: October 2005

We used a selective adaptation procedure to investigate the possibility that differences in the degree to which stimuli within a phonetic category are considered to be good exemplars of the category—that is, differences in perceived category goodness—have a basis at a prephonetic, auditory level of processing. For three different phonetic contrasts (/b–p/, /d–g/, /b–w/), we assessed the relative magnitude of adaptation along a stimulus continuum produced by a variety of stimuli from the continuum belonging to a given phonetic category. For all three phonetic contrasts, nonmonotonic adaptation functions were obtained: As the adaptor moved away from the category boundary, there was an initial increase in adaptation, followed by a subsequent decrease. On the assumption that selective adaptation taps a prephonetic, auditory level of processing, these findings permit the following conclusions. First, at an auditory level there is a limit on the range of stimuli along a continuum that is treated as relevant to a given contrast; that is, the stimuli along a continuum are effectively grouped into auditory categories. Second, stimuli within an auditory category vary in their effectiveness as category members, providing an internal structure to the categories. Finally, this internal category structure at the auditory level, revealed by the adaptation procedure, may provide a basis for differences in perceived category goodness at the phonetic level.
The effect of a hearing aid on the speech-reception threshold of hearing-impaired listeners in quiet and in noise
Authors: Duquesnoy A. J. , Plomp R.
Published: October 2005

The monaural free-field speech-reception threshold (SRT) without and with a hearing aid was investigated for conversational sentences presented to 50 hearing-impaired listeners. SRT without a hearing aid was measured in quiet and in noise at levels of 40, 55, 70, and 85 dBA. SRT with a hearing aid was obtained in quiet and at noise levels of 25, 40, 55, and 70 dBA. The noise had a long-term average spectrum equal to that of the sentences. The 50 subjects were equally distributed over five degrees of pure-tone hearing loss and five types of hearing impairment (sensorineural high-frequency losses, with or without recruitment; flat audiogram of a sensorineural, mixed, or conductive origin). It is shown that a model of SRT as a function of noise level, developed by Plomp [J. Acoust. Soc. Am. 63, 533–549 (1978)] gives a good description of the SRT values measured, both without and with a hearing aid. The data illustrate that, generally, current hearing aids do not improve speech intelligibility in noise beyond, roughly, 60 dBA.
Effect of mounting constraints on the response of piezoelectric disks
Authors: Bogy D. B. , Su R. T-K.
Published: October 2005

An experimental investigation was conducted to determine the effects of different edge conditions and face mount backing conditions on the electrical response of strongly coupled piezoelectric disks with electroded faces on which spatially nonuniform forces are applied by a pencil lead breaking mechanism. Various mounting schemes were employed to simulate traction-free, simply supported, and fixed edge conditions. The response was found to be relatively insensitive to changes in the edge conditions. Experiments were also conducted on a commercially available transducer in various stages of dismantlement. It was revealed that the main structural element for controlling the electrical output was the impedance matched backing that is epoxied to the inner face of the crystal. It was concluded that mathematical models for characterizing transducers subject to nonuniform face loadings can incorporate the analytically most convenient edge conditions but must also include a suitable model for the backing.
Acoustic shadowing by an isolated seamount
Authors: Chapman N. Ross , Ebbeson Gordon R.
Published: October 2005

Acoustic shadowing by an isolated seamount has been studied by examining the multipath propagation measurements obtained in a shot run that passed over the seamount peak. Source depths of 24 and 196 m were used in the experiment. In the acoustic shadow, the propagation loss for the shallow 24-m shots increased by 10–15 dB over the loss expected in the absence of the seamount. Examination of the pressure-time history for shots deployed in the shadowing region revealed that the signals consisted of two components. The first and dominant pulse was determined to be a diffracted wave which passed over the seamount by rough-surface forward scattering and diffraction. The subsequent group of weaker pulses was attributed to the energy which had passed over the seamount by a series of surface–bottom interactions. The shadowing loss increased by 3 dB per octave for frequencies greater than 50 Hz, in agreement with theory, but is appreciably greater than the predicted values at lower frequencies. The shadowing loss for the 196-m shots was about 5 dB less than that observed for the shallower shots.
Deconvolution of the fish scattering PDF from the echo PDF for a single transducer sonar
Authors: Clay C. S.
Published: October 2005

The purpose of this paper is to deconvolve the beam pattern effect from the amplitude distribution of sonar echoes from fish to determine the scattering processes at fish. The paper is a continuation of our acoustic methods to measure fish abundance. It demonstrates a direct procedure for determining the fish density (fish/m3), the probability density function (PDF) of scattering processes at fish, and the PDF of echoes. The procedure uses nonoverlapping echoes from a single transducer sonar system. The integral equation for the echo PDF is in Clay and Medwin [Acoustical Oceanography (Wiley, New York, 1977), pp. 476–482]. It relates the PDFs of the sonar output wE(e), transducer beam wT(b), and scattering process at the fish wF(e). I use the transformations b=exp(−x) and e=e0 exp(−y) to change the integral to the standard form of the convolution integral. The derivation of expressions of the convolution and deconvolution using z transformations follow directly. We use a ‘‘home-style’’ microcomputer for computations. Tests of the deconvolution technique on fish echo PDFs for Lake Michigan alewife show the presence of the alewife (10–12 cm length) and an unidentified group of larger fish having two to three times the length of the alewife. Deconvolution of Lake Superior data for 1978 indicate the presence of smelt and an unknown group of larger fish. Deconvolution of 1979 Lake Superior data gives an echo PDF that can be attributed to smelt. In both lakes, fish density estimates are between 10−4 and 10−3 fish/m3.
Dependence of ultrasonic propagation velocities and transit times on an electric biasing field in alpha quartz
Authors: Kittinger Erwin , Reider Georg A. , Tichý Jan
Published: October 2005

The variation of the velocity of elastic waves and of ultrasonic transit times with the direction of propagation under the influence of an externally applied dc electric field was calculated on the basis of known elastic constants and recently determined effective electroelastic moduli for alpha quartz. Results are presented in graphical form for propagation directions in the three planes defined by the conventional Cartesian crystal axes. For each propagation direction the three possible acoustic modes are considered in conjunction with three mutually perpendicular field configurations.
Dynamic Young’s moduli of some commercially available polyurethanes
Authors: Capps Rodger N.
Published: October 2005

The Young’s modulus and loss tangent have been measured in air for a number of commercially available polyurethanes. A resonance technique was used for measurements over the approximate frequency range 102 to 104 Hz and the approximate temperature range 40° to −5 °C. Master curves and Williams–Landel–Ferry shift constants were detemined for the materials tested. The automated data acquisition system used is described. The experimental procedure was found to be a reliable method for determining the viscoelastic constants for extensional wave propagation in elastomeric materials.
Sampling strategies for monitoring noise in the vicinity of airports
Authors: Schomer P. D. , DeVor R. E. , Kline W. A.
Published: October 2005

This paper is the third in a series dealing with the development of temporal sampling strategies for estimation of mean noise levels in the vicinity of airports. It extends the previous analysis for westcoast, one-direction airports (due to prevailing winds) to eastcoast, multidirection airports (Boston Logan, Washington Dulles, and National). The results show that the data for many of the eastcoast airport sites are nonstationary in the mean level and the corresponding consecutive sampling requirements predicted by the Dynamic Data System (DDS) methodology are very large, at times exceeding 1/3 of a year. When the data are stationary, Monte Carlo simulations using the data produce sampling requirements comparable to the values obtained by the DDS methodology. However, the DDS methodology tends to overestimate sampling requirements for nonstationary data. The simulations demonstrate that nonconsecutive sampling strategies reduce the overall sampling requirements for nonstationary data. In general, the results reveal the following: (a) Westcoast (one-direction); ±50% precision—four weeks, any sampling strategy, ±35% precision—eight weeks, any sampling strategy. (b) Eastcoast (multidirection); ±60% precision—four weeks, one from each quarter, ±40% precision—eight weeks, one from each eighth.
An analytical model for the detection performance of multiple channel time history display formats
Authors: Delisle R. B. , Kroenert J. T.
Published: October 2005

An analytical model for the detection performance of multiple channel time history display formats such as used with multibeam systems and spectrograms is presented. The resulting receiver operating characteristic (ROC) curves are presented as a function of the number of lines displayed. A typical comparison with the simple threshold excess decision rule operating on the same data is also presented.
Magnitude and phase-frequency response to single tones in the auditory nerve
Authors: Allen Jont B.
Published: October 2005

In this paper we describe magnitude and phase measurements obtained from primary single unit recordings in the cat auditory nerve. Levels range from threshold to 100 dB SPL, with frequencies from 0.1–30.0 kHz. The upper limit on the phase measurements was limited by the loss of neural phase locking at 4–5 kHz. For each unit, the frequency tuning curve (FTC) was measured by the method of Kiang and Moxon [M. C. Liberman, J. Acoust. Soc. Am. 63, 442–445 (1978)] to establish the threshold frequency response of the unit. Data from several selected animals, organized by characteristic frequency (CF), are presented showing phase response, group delay, frequency tuning, and tuning slope for each CF range. The major emphasis in this paper is on the ‘‘linear’’ aspects of the data as characterized by the filter properties of the single unit response, however a number of nonlinear (level-dependent) effects are described. Data are presented showing the phase response normalized by the chochlear microphonic (CM) recorded at the round window membrane. This normalization simplifies the phase data since it produces a constant phase slope with respect to frequency (constant group delay) for high CF units ( fCF>1 kHz) for frequencies more than one octave below their characteristic frequencies. A model of CM, as measured at the round window (RW), is presented and compared to experimental CM measurements. The CM model gives a reasonable fit to the experimental data above 500 Hz. Our interpretation of the CM normalization is that it removes driver and middle ear effects. In the model we assume that the CM is generated by the displacement of the basilar membrane near the round window recording site.
Chinchilla auditory-nerve responses to low-frequency tones
Authors: Ruggero Mario A. , Rich Nola C.
Published: October 2005

Single unit activity was recorded in the auditory nerves of chinchillas. Period histograms were constructed for responses to tones with frequencies 30–1000 Hz. For low-frequency tones at near-threshold levels, peak period histogram phases for low- and medium-best-frequency (BF) neurons (≤3 kHz) ranged from synchronous with condensation at the eardrum to 90° leading it. At near-threshold (but high absolute) levels, high-BF (≥8 kHz) neurons responded in phase with rarefaction. At even higher levels, period histograms for responses of high-BF neurons tended to become bimodal, with one of the modes lagging rarefaction by 90°. Using cochlear microphonics as an indicator of basilar membrane (BM) displacement, at threshold levels, response phase of low- and medium-BF neurons fall within a range between displacement and velocity of the BM toward scala vestibuli. High-BF neurons respond, at threshold (but high) intensities, in phase with BM displacement toward scala tympani. The rates of growth of frequency sensitivity in responses of low-BF (+18 dB/oct) and high-BF (+12 dB/oct) neurons are consistent with preferred response phases corresponding to BM SV velocity and ST displacement, respectively. At supra-threshold levels high-BF neurons may fire preferentially to both scala tympani displacement and scala vestibuli velocity. These results support the notion that, for high-intensity, low-frequency stimuli, OHC hyperpolarization can induce excitation of the dendrites innervating IHCs.
Coherent attenuation of acoustic waves by pair-correlated random distribution of scatterers with uniform and Gaussian size distributions
Authors: Varadan V. K. , Bringi V. N. , Varadan V. V. , Ma Y.
Published: October 2005

Acoustic wave attenuation due to multiple scattering in a two-phase medium consisting of a fluid with embedded rigid, fluid, or elastic particles of varying sizes is discussed. The formulation, involving the exciting and scattered fields of an incident acoustic plane wave, is based on the T-matrix method. The propagation features of coherent waves in the mixture are described by the dispersion equation which is derived by applying standard statistical approximations to the discrete random medium. Special attention is focused on the pair-correlation function between the scatterers using the self-consistent approximation (SCA) which seems better than the Percus-Yevick approximation (PYA) when the volume fraction becomes significant. Besides deriving low-frequency analytical results for coherent wave speed and attenuation, the dispersion equation has been solved numerically for higher frequencies for particles with uniform and Gaussian size distributions.
Propagation in air of N waves produced by sparks
Authors: Wright Wayne M.
Published: October 2005

Weak sparks, of length 0.5–1.0 cm and energy per discharge 0.01–0.1 J, served to produce intense acoustic transients resembling N waves. Amplitude decay and waveform elongation were studied, for propagation distance up to 2 m, through the use of a wideband capacitor microphone with essentially uniform response from dc to 1 MHz. Within the range of propagation distances for which the first (compression) phase of the N wave was completely formed, the duration of this compression phase T and its amplitude ps were found to agree with the theoretical relations T=T0[1+σ0 ln(r/r0)]1/2 and ps =(r0 ps 0/r)[1+σ0 ln(r/r0)]−1/2, where σ0 is a parameter that depends upon the values of ps and T at a reference distance from the source r0. The time required for the amplitude of the head shock to increase from 5% to 95% of peak value was observed to vary from 0.45 μs (imposed by the microphone response) to greater than 2.0 μs as the wave traveled outward and as its amplitude decreased. Finally, the microphone was calibrated through use of the variation with distance of measured values of T; this new method has led to calculation of a free-field sensitivity that agrees within ±1 dB with the results of other calibrations.
Time domain study of the terminated transient parametric array
Authors: Pace Nicholas G. , Ceen Robert V.
Published: October 2005

A spatial impulse response model of the parametric array is developed and used to give physical insight into its behavior when operated in a transient mode. Experimental measurements of the spatial dependence of the acoustic pressure waveforms produced by the transient parametric array are compared with the result of the convolution of the spatial impulse response with the specific pressure waveforms used. Particular emphasis is given to the case where the primary field is discontinuously terminated. In such cases effects due to the finite aperture of the parametric array and effects due to its termination may be seen by a point hydrophone either as separated or superposed events in time, depending on the geometry, when the parametric array is operated in the transient mode. Although the impulse response model is restricted by various assumptions, it can contribute to an understanding of the parametric array operation under more general circumstances.
An intrinsically irreversible thermoacoustic heat engine
Authors: Wheatley John , Hofler T. , Swift G. W. , Migliori A.
Published: October 2005

Certain thermoacoustic effects are described which form the basis for a heat engine that is intrinsically irreversible in the sense that it requires thermal lags for its operation. After discussing several acoustical heating and cooling effects, including the behavior of a new structure called a ‘‘thermoacoustic couple,’’ we discuss structures that can be placed in acoustically resonant tubes to produce both substantial heat pumping effects and, for restricted heat inputs, large temperature differences. The results are analyzed quantitatively using a second-order thermoacoustic theory based on the work of Rott. The qualities of the acoustic engine are generalized to describe a class of intrinsically irreversible heat engines of which the present acoustic engine is a special case. Finally the results of analysis of several idealized intrinsically irreversible engines are presented. These suggest that the efficiency of such engines may be determined primarily by geometry or configuration rather than by temperature.
Evaluation of a tactile vocoder for word recognition
Authors: Brooks P. L. , Frost B. J.
Published: October 2005

Normal subjects learned to identify words through a tactile vocoder. The vocoder employed 16 filter channels, each with a bandwidth of 1/3 octave, with center frequencies ranging from 200–8000 Hz. The output of each filter was detected and after logarithmic amplification the resulting outputs were transmitted to a 16-channel solenoid array placed on the subject’s ventromedial forearm. Words, spoken ‘‘live voice,’’ were used as stimuli; the subject was able to feel both the vocalizations of the reader and herself and, most importantly, extensive training was provided. In 40.5 h one subject learned 70 words and a second subject reached criterion on 150 words in the comparatively short time of 55 h. Words that were poorly identified initially were identified more readily with increased experience. Phonetic identification tests showed that the features of voicing, nasality, and frication were reliably recognized, indicating the tactile vocoder will be useful in providing information to complement lipreading. Finally, subjects learned rapidly to generalize word-learning to unfamiliar readers.
Effect of source-motion-induced transmission fluctuations in intersensor correlation
Authors: Doles J. H.
Published: October 2005

An asymptotic mode representation of the signal field radiated by a narrow-band source executing slow horizontal motion has been developed. An approximation to this representation has been used to estimate the amount of coherent correlation between the signals received at two sensors after an appropriate adjustment has been made to account for time delay and Doppler difference. A calculation of intersensor coherent correlations for a specific scenario indicates that there can be significant coherent correlation degradation when the signal received at one (or both) of the sensors has faded. This degradation is due to amplitude and phase fluctuations caused by interference between modes.
Acoustic dispersion in a deep ocean channel
Authors: Gerlach Albert A. , Flowers Kenneth D. , Johnson Robert B.
Published: October 2005

Acoustic dispersion in a deep ocean channel is characterized by the dependence of sound propagation speed on signal frequency along the axial propagation path. A model normal-mode solution of the wave equation is employed to compute the acoustic field for sinusoidal signals as a function of both axial range and frequency. A virtual propagation time is defined which reflects the range-dependent phase of the acoustic field. When signals of different frequency are transmitted, the remotely observed frequency ratio (for a given range rate) will fluctuate about the true frequency ratio of the transmitted signals. The magnitude of the fluctuation is directly proportional to the true frequency ratio. A measure of the spectral dispersion is defined as the difference between the observed and true frequency ratios. The dependence of this measure on range and signal frequencies (for a given frequency ratio) is determined to be relatively insignificant. It is concluded that acoustic dispersion in a deep ocean channel is microscopic in its measure, but it can be significant for applications involving the phase correlation of broadband (or spectrally separated) signals over long time intervals.
Slope propagation: Mechanisms and parameter sensitivities
Authors: Koch Robert A. , Rutherford Steven R. , Payne Susan G.
Published: October 2005

An adiabatic normal mode analysis is used to identify cylindrical spreading, renormalization, bottom attenuation, differential mode excitation and reception, and mode cutoff as major physical mechanisms influencing underwater acoustic propagation over slopes. Propagation is sensitive to the shallow water sediment attenuation but not to the slope angle.
Perturbations in travel time and ray geometry due to mesoscale disturbances: A comparison of exact and approximate calculations
Authors: Spiesberger John L. , Worcester Peter F.
Published: October 2005

Exact calculations of the changes in eigenray travel time and geometry, due to range-dependent mesoscale disturbances, are compared to three approximations. In the first approximation, the sound-speed perturbation is integrated along the unperturbed path. In the second approximation, the range average of the sound-speed perturbation is integrated along the unperturbed path. The third approximation uses the range-average raytrace to estimate changes of travel time and geometry. Calculations made both for a measured section through a mesoscale eddy and for a simplified model of an eddy (with variable strength, position, and boundary width) suggest that: (i) while none of the approximations tested is uniformly the best, the first approximation is to be preferred ; (ii) the eddy position relative to the ray path is quite significant; and (iii) the exact travel-time perturbations are not sensitive to whether the eddy boundaries are assumed sharp or gradual. For an eddy perturbation of ±9 m/s (±1.9 °C or Rossby wave displacement of about ∓200 m) at 700-m depth, the travel-time approximations are typically in error by 10%–20%. The associated change in turning depth from the unperturbed state to either the perturbed or the range-average state is typically ±100–200 m. These errors are significant, but not large, and suggest that it will be beneficial to iterate linear inverse schemes used to estimate sound-speed perturbations from travel-time perturbations.
Concurrent underwater acoustic wave front fluctuations at two frequencies over a 75-nmi path
Authors: Wagar J. L.
Published: October 2005

An experiment was performed to investigate the fluctuations in wave front shape of signals transmitted over a distance of about 75 nmi from a ship-suspended sound source to a bottomed set of receivers. An experimental set of eight receivers, spanning a distance of about 2300 ft in both the downslope and cross-slope directions, was laid on a 26° slope southwest of Bermuda at about 5000-ft depth. Pulses of 200- and 400-Hz signals were transmitted alternately from the projector, by the second-order RSR mode; these were recorded on an oscillograph, and delays in arrival time at each receiver were measured. Plane wave fronts were fitted to the delay data, and the azimuth and elevation angles for the wave fronts were calculated. The effect of ship motion and stationary effects were removed from the raw delays. Plane wave front fits to the adjusted data were made, and deviations from these wave fronts were found for each receiver. The wave fronts are characterized by two actions: (1) gross wave front rocking and tilting, and (2) crinkling of the wave front (short-scale effects, a dimension smaller than the maximum receiver spacing).
Spectral spread of sea-surface reverberation
Authors: McDaniel Suzanne T. , Gorman Arthur D.
Published: October 2005

In a recent paper [S. T. McDaniel and A. D. Gorman, J. Geophys. Res. 87 (1982)] subsurface bubbles were identified as the dominant mechanism responsible for high-frequency surface reverberation. In this paper, expressions are obtained that directly relate the spectral spread of the scattered signals to the ocean wave-height frequency spectrum. For frequencies above 20 kHz, the spectra are found to be Gaussian. A normalized spectral spreading width is defined, and its dependence on oceanographic and systems parameters is discussed. A comparison with representative acoustical data confirms the theoretical predictions.
A statistical analysis of surface reverberation
Authors: Wilson Gary R.
Published: October 2005

A statistical analysis of reverberation generated by projecting sound at the wind-driven surface of a freshwater lake is presented. One test for randomness, two tests for homogeneity, and four tests for normality were employed in the analysis. The hypothesis tests were applied at various times during the duration of the reverberation. Procedures to combine the test results to provide an assessment of the test hypothesis over the duration of the reverberation are presented. These results indicated that the reverberation was non-Gaussian, a finding in contrast to the results of previous studies. The non-Gaussian nature of reverberation may result in degraded performance of signal processing algorithms that assume a Gaussian noise field and operate in a reverberant environment.
Generalized reaction principles and reciprocity theorems for the wave equations, and the relationship between the time-advanced and time-retarded fields
Authors: Bojarski Norbert N.
Published: October 2005

Generalized reaction principles and generalized reciprocity theorems for the scalar and vector wave equations are derived. It is shown that the reaction principles of Rumsey [Phys. Rev. 94, 1483–1491 (1954)] and the reciprocity theorems of Welsh [IRE Trans. Antennas Propag. 8(1), 68–73 (1960)] are special cases of these generalized reaction principles and generalized reciprocity theorems. The generalized reciprocity theorems are cast in terms of the time-retarded fields only, as well as in terms of the time-retarded and time-advanced fields. It is shown that the advanced fields are an improper solution of the wave equations subject to the proper Sommerfeld radiation boundary conditions at infinity. A relationship between the time-advanced and time-retarded fields is derived.
A technique for improving detection and estimation of signals contaminated by under ice noise
Authors: Dwyer Roger F.
Published: October 2005

Recent analyses of FRAM II arctic data have shown that under ice ambient noise can be at times highly impulsive and non-Gaussian. The analyses included time domain statistical measurements which were consistent with previously reported results of experiments made within the Canadian Arctic Archipelago. New findings in the frequency domain based on skew, kurtosis, and cumulative distribution function estimates, also indicate the existence of strong non-Gaussian noise. It is known that the ability to detect and estimate signals contaminated with non-Gaussian noise using conventional processing is degraded compared with optimum techniques which utilize knowledge of the noise statistics. Results comparing the performance of conventional and nearly optimum signal processing methods are presented using the FRAM II data.
Sound radiation from an impact-excited clamped circular plate in an infinite baffle
Authors: Akay Adnan , Latcha Michael
Published: October 2005

Sound radiation from most mechanical systems results from impact forces of various kinds. In this paper, transient sound radiation from impact-excited circular plates is studied both analytically and experimentally. First, the contact force developed during the inelastic collision of a ball with a flexible plate was obtained. The plate vibrations were then obtained using normal mode analysis. The sound radiation waveforms in the time domain were obtained by numerical integration of the Rayleigh integral. Both analytical and experimental results show the radiation of a sound pulse during the contact which is a result of the forced deformation of the plate. Quantitative relationships are given for the plate vibration response and acoustic radiation.
An extended unitary approach for acoustical scattering from elastic shells immersed in a fluid
Authors: Werby M. F. , Green L. H.
Published: October 2005

We derive equations using the T-matrix approach for acoustical scattering from elastic shells immersed in a fluid. The equations contain unitary and symmetry constraints and afford a new procedure for the calculation of the T matrix. The technique, in addition to satisfying symmetry and unitary conditions, proves to be more numerically stable and less time consuming than the conventional method. In addition, the procedure enables one to determine if convergence has been satisfied and in the limit of no convergence, proves to be a better approximation than that of the matrix method. We have developed computer codes using the new technique and present comparisons with the conventional procedure. A salient feature of the new technique is that convergence is arrived at with a smaller number of expansion terms than the older method and this is particularly true as the aspect ratio of the target is increased.
Effects of auditory fatigue on speech intelligibility and lexical decision in noise
Authors: Sorin C. , Thouin-Daniel C.
Published: October 2005

The influence of weak auditory fatigue on speech identification and lexical decision (word/nonword) was studied. It appears that, at a low listening level and in presence of a strong masking noise, auditory fatigue gives rise to : (1) a decrease in identification scores, (2) more frequent confusions for fricatives, (3) a reduction in correct lexical decision scores, (4) an increase in the tendency to respond ‘‘word’’ more often than ‘‘nonword,’’ (5) a slight increase in reaction times for incorrectly repeated items. The intelligibility impairment can be attributed to a combination of masking and fatigue effects. Errors in lexical decisions and changes in response times are explained by an adaptation of the lexical decision processes to the degraded perceptual representations of the stimuli. There is no clear evidence in this experiment that a very central component of auditory fatigue influences lexical decisions.