bluuebunny/crossref_metadata_2025 huggingface dataset:
Scattering of an acoustic Gaussian beam from a fluid–solid interface
Authors: Pott John , Harris John G.
Published: October 2005

The reflection and refraction at a fluid–solid interface of an acoustic beam, whose amplitude is Gaussian in cross section and which oscillates harmonically in time, is studied. The incident and scattered beams are constructed using the complex source-point method. The incident beam is specularly reflected except at angles near one of the critical angles, of which the Rayleigh angle is the most important. Near this angle the beam excites both a leaky Rayleigh wave and a reflected beam, and the interference between these two disturbances produces the beam shifting noted by other workers. Surprisingly, a backward-traveling leaky Rayleigh wave is also excited, although its amplitude is quite small. The incident beam, near normal incidence, is refracted into a compressional beam and a shear beam, both of whose amplitudes are Gaussian in cross section. Whereas the incident beam has a circularly shaped cross section, both transmitted beams have elliptically shaped cross sections. Moreover, the transmitted beams spread rapidly so that the compressional and shear beams always overlap. This rapid spreading limits the resolution of ultrasonic probes used to find cracks or other defects in a solid.
Low-frequency grazing propagation over periodic steep-sloped rigid roughness elements
Authors: Medwin Herman , D’Spain Gerald L. , Childs Emily , Hollis Stephen J.
Published: October 2005

Extensive experimental studies of the coherently forward scattered sound at grazing incidence to low roughness rigid surfaces with periodic steep-sloped elements have confirmed several of the theoretical predictions of large boundary wave amplitude and subsonic dispersion [Tolstoy, J. Acoust. Soc. Am. 75, 1–22 (1984)]. For example, at short ranges the boundary wave amplitude diverges cylindrically and is proportional to εk3/2r−1/2, where ε is the scattering parameter, k is the wavenumber, and r is the range; thereby, at sufficient ranges and frequencies it exceeds the amplitude of the spherically diverging direct wave. The dispersion is subsonic and goes as Ak2ε2, where A depends on the roughness element. The experiments have also revealed an attenuation factor exp (−δr), where δ=αk6 due to incoherent scatter up to critical range kr=π/(Ak2ε2) beyond which an attenuation of form exp (− 1/2 A2ε4k6r2) becomes dominant. This leads to frequency-independent peak amplitudes two to six times the direct wave amplitude for the surfaces studied. Beyond this critical, frequency-dependent, range the boundary wave catastrophically self-destructs due to interference. The amplitude, dispersion, and attenuation of the boundary wave is a function of the packing, heights, and slopes or shapes of the scattering elements. Results are presented for spheres, spaced and packed circular cylinders, and several wedge corrugated roughness elements. The boundary wave is also shown to diffract over a ridge in the same manner as the direct wave from a point source.
Modified sound refraction near a rough ocean bottom
Authors: Medwin Herman , Novarini Jorge C.
Published: October 2005

It is well established that there is a strong boundary wave during low-frequency grazing scatter at a rough rigid surface overlaid by a homogeneous medium. Tolstoy [J. Acoust. Soc. Am. 69, 1290–1298 (1981)] has also shown that when source and receiver are on the bottom and the velocity in the medium decreases away from the ocean bottom the boundary wave tunnels into the shadow zone. We consider the case when source and receiver are near the ocean surface. It is predicted that, under certain conditions of velocity gradient, frequency and bottom roughness, the addition of the boundary wave mode to the volume wave mode will change the path of the grazing specularly scattered ray above the rough bottom. As a result, an upward refracted ray will reach the surface at a skip distance significantly greater than for a smooth bottom. This modified refraction phenomenon should be detectable at sea, under suitable indicated experimental conditions.
A range refraction parabolic equation
Authors: Tappert Frederick D. , Lee Ding
Published: October 2005

Application of the standard parabolic wave equation to solve real problems requires a clever selection of the reference wavenumber k0. An extended parabolic equation, having range refraction capability, is reintroduced in such a manner so as to be totally independent of k0. An already existing Implicit Finite-Difference (IFD) model was applied to test the range refraction parabolic equation. Results compare favorably with known solutions for weakly range-dependent environments, but yield significant corrections for propagation through strong oceanic fronts.
A statistical approach to determining the number density of random scatterers from backscattered pulses
Authors: Wilhelmij Paul , Denbigh Philip
Published: October 2005

This paper describes a method of using the statistical character of the waveform backscattered from random scatterers to estimate the scatterer number density. The moments of the probability density function of the backscattered intensity depend on the scatterer number density. Expressions exist for these moments in terms of the number of scatterers contributing to the echo signal. These expressions can give an estimate for the scatterer number density, provided the resolution cell size of the backscattering configuration is known, and provided the number of scatterers in the resolution cell is small. This latter constraint is equivalent to a requirement that the statistics of the return signal envelope deviate significantly from a Rayleigh distribution. The validity of these expressions is investigated by analyzing the acoustic waveform backscattered from a randomized volume distribution of polystyrene spheres suspended in water when insonified by a short acoustic pulse. Experimentally, the second-order moment of intensity is found to be given the most accurate predictions of number density. A specific application suggested for this work is acoustic fish-stock assessment. Other possible applications are ultrasonic tissue characterization and acoustic ocean bottom identification.
Pulsed parametric array
Authors: Trivett D. H. , Rogers Peter H.
Published: October 2005

An earlier investigation [J. Acoust. Soc. Am. 71, 1114–1117 (1982)] of the nonlinear interaction of a freely propagating pulse with a cw plane wave is extended to encompass the pulsed parametric array. We find that a scattered signal at the difference frequency is received in the farfield only during the time that a signal is received from the stationary boundary (i.e., the interaction region directly in front of the transducer). Once the pulse appears to have left the face of the transducer in that no further signal is received from the stationary boundary, no further signal at the difference frequency is observed in the farfield. This results in an observed scattered signal that has a pulse length and arrival time consistent with direct radiation from the face of the transducer. However, the signal is found to be generated by a virtual endfire array with an effective length dependent upon the pulse length and observation angle. Experimental evidence is presented in support of these results.
An evaluation of the effectiveness of three hearing protection devices at an industrial facility with a TWA of 107 dB
Authors: Royster Larry H. , Royster Julia Doswell , Cecich Thomas F.
Published: October 2005

Three hearing protection devices [Siebe Norton Com-fit earplug, Flents Silenta model 080 earmuff, and E-A-R■ foam earplug] were compared for their effectiveness in preventing both daily temporary threshold shifts (TTS) and threshold variability between sequential annual audiograms for workers in an industrial environment with a TWA of 107 dB. Com-fit wearers showed significant TTS at 500–4000 Hz from the beginning to the end of the workday. Silenta wearers displayed significant TTS at 500 Hz and nonsignificant improvement at 6000 Hz. E-A-R wearers showed significant TTS at 1000–2000 Hz and nonsignificant improvement at 3000–6000 Hz. Statistical analysis indicated that the protection provided by the E-A-R plug was significantly better than that of the Com-fit plug at 500–4000 Hz, and significantly better than the protection of the Silenta muff at 500, 3000, and 4000 Hz. Employees’ last four annual audiograms prior to the start of the TTS study were evaluated to compare the wearer groups’ mean values of the %BWs statistic (sequential percent better or worse). Previous research indicates that the %BWs statistic for a properly protected population with past audiometric test experience will be less than 30%. The E-A-R group showed an acceptable %BWs value (26%), but the Silenta wearers (45%) and Com-fit wearers (53%) showed excess threshold variability in threshold measurements from year to year.
The synoptic sound-speed field of a warm-core Gulf Stream ring
Authors: Bisagni James J. , Cornillon Peter
Published: October 2005

A synoptic expendable bathythermograph survey of the warm-core Gulf Stream ring 81-D, conducted in September 1981 when the ring was located 550 km south of Halifax, Nova Scotia, provided the basis for a detailed study of the ring’s sound-speed field. Salinities used for computing sound speed were derived from nonsynoptic conductivity–temperature–depth data collected during the survey. Analysis of the sound-speed field, using vertical and horizontal sections and satellite imagery, revealed the ring’s typical high sound-speed core, but also showed increased horizontal and vertical gradients along the ring’s western margin as compared to its eastern side. This asymmetry appears to be related to a surface streamer of warm, higher sound-speed Gulf Stream water overlying colder, lower sound-speed slope water, resulting in a subsurface sound duct centered 100 m below the surface along the ring’s western margin. The subsurface duct and increased vertical gradient resulted in 30–50 dB greater loss at depths of 100 and 200 m in the ring’s eastern margin as compared to its western side and center. Strong ray channeling and refraction of a 2000-Hz source at a depth of 100 m was also noted. Based on these observations and predictions, warm-core rings may possess regions of increased acoustic range dependence due to the interactions of waters along their margins.
Converging uniaxial strain shock waves in nonlinearly locking solids under loading–unloading blasts. II: All-events method of integration along with the existing waves
Authors: Ziv M.
Published: October 2005

A computational method is developed for the wave characteristics formulation governing transient nonlinear deformations of locking solids where waves of a moderate unloading process overtake a shocked precursor wave of large uniaxial strain. The unique feature of the proposed all-event integration scheme is that in order to evaluate the unknowns at a space–time point, not only past events are considered, but also present events surrounding the point in question are accounted for. Moreover, the solution by the proposed method propagates along all existing waves inside a variable space–time grid formed by the bicharacteristic curves associated with the chord-shock speed of the leading wave (precursor). Based on these features, the method is essentially analytical where in its final stage of development a straightforward numerical integration is required which is free of iteration procedures, stability criteria, and of any other numerical analysis.
Converging uniaxial strain shock waves in nonlinearly locking solids under loading–unloading blasts. III: Resultant deformation
Authors: Ziv M.
Published: October 2005

Part III deals with the nonlinear transient response of an elastic-plastic locking half-space traversed by converging waves of uniaxial large strain generated as a result of a uniform loading–unloading blast suddenly applied with no rise time to the entire surface of the half-space. For this type of boundary-value problem where a shocked leading wave interacts continuously with faster overtaking unloading waves, a computational method was developed based on the theory of characteristics. This method, which employs an all-events integration process propagating along the existing wavelets, is essentially analytical. In its final stage of the solution, a straightforward numerical integration is required free of iteration procedures, stability criteria, and any other numerical analysis. The resultant response of the half-space is described and interpreted here.
Regional differences in the cyclic variation of myocardial backscatter that parallel regional differences in contractile performance
Authors: Mottley Jack G. , Glueck Robert M. , Perez Julio E. , Sobel Burton E. , Miller J. G.
Published: October 2005

Previous reports from our laboratory indicate that ultrasonic backscatter from myocardium exhibits a cyclic variation during the cardiac cycle that is reduced sharply by ischemia, a process which impairs both systolic contraction and diastolic relaxation. These results suggest that the cyclic variation of backscatter may be related to the cyclic variation of the contractile performance of the myocardium. Because contractile performance of the left ventricle is known to exhibit regional variability, the present study was undertaken to determine whether such regional differences in contractile performance are paralleled by differences in the magnitude of the cyclic variation of ultrasonic backscatter. Measurements obtained from representative zones of three regions of the hearts of ten open-chest dogs indicate that the magnitude of the cyclic pattern of variation of backscatter parallels the regional differences in contractile performance throughout the left ventricle with the maximum variation (5.5±0.9 dB peak-to-peak amplitude) occurring at the apex, intermediate values (4.3±0.8 dB) at the midwall, and minimum (0.5±1.0 dB) at the base. These results suggest that the ultrasonic backscatter may be sensitive to the regional myocardial contractile performance.
Perceiving vowels in the presence of another sound: Constraints on formant perception
Authors: Darwin C. J.
Published: October 2005

Speech is normally heard against a background of other sounds, yet our ability to isolate perceptually the speech of a particular talker is poorly understood. The experiments reported here illustrate two different ways in which a listener may decide whether a tone at a harmonic of a vowel’s fundamental forms part of the vowel. First, a tone that starts or stops at a different time from a vowel is less likely to be heard as part of that vowel than if it is simultaneous with it; moreover, this effect occurs regardless of whether the tone has been added to a normal vowel, or to a vowel that has already been reduced in energy at the tone’s frequency. Second, energy added simultaneously with a vowel, at a harmonic frequency near to the vowel’s first formant, may or may not be fully incorporated into the vowel percept, depending on its relation to the first formant: When the additional tone is just below the vowel’s first formant frequency, it is less likely to be incorporated than energy that is added at a frequency just above the first formant. Both experiments show that formants may only be estimated after properties of the sound wave have been grouped into different apparent sound sources. The first result illustrates a general auditory mechanism for performing perceptual grouping, while the second result illustrates a mechanism that may use a more specific constraint on vocal-tract transfer functions.
Harmonic-intensity analysis of normal and hoarse voices
Authors: Hiraoka Nobuaki , Kitazoe Yasuhiro , Ueta Hisashi , Tanaka Shinzo , Tanabe Masahiro
Published: October 2005

Objective evaluation of normal and hoarse voices is performed considering the characteristic that hoarse voices show a prominent fundamental frequency intensity compared with harmonics in the voice spectrum. The relative harmonic intensity Hr, obtained from a stable portion of the sustained vowel /a/, is defined as the intensity of the second and higher harmonics expressed as a percentage of the total voice intensity. Ninety-five percent of the normal voices examined have Hr larger than the critical value of 67.2%, whereas 90% of the hoarse voices have Hr smaller than the critical value. The harmonic-intensity analysis thus provides good discrimination between normal and hoarse voices.
Which syllable does an intervocalic stop belong to? A selective adaptation study
Authors: Samuel Arthur G. , Kat Donna , Tartter Vivien C.
Published: October 2005

Three selective adaptation experiments were conducted to investigate whether intervocalic stops are perceived as the end of the preceding syllable or as the beginning of the following one. The pattern of adaptation effects (and just as importantly, noneffects) indicated that intervocalic stop consonants are perceptually more like syllable-initial than syllable-final ones. From this it might be concluded that the perceptual system breaks down a vowel–consonant–vowel (VCV) utterance into a V–CV sequence. However, the similarity of an intervocalic stop to a syllable-initial one is quite limited; the consonant in a VCV is apparently treated as essentially different from consonants in either VC or CV utterances. These results clarify, and perhaps complicate, the role of the syllable in models of the speech perception process.
A multispeaker analysis of durations in read French paragraphs
Authors: O’Shaughnessy Douglas
Published: October 2005

Understanding how the durations of acoustic segments vary in natural language can lead to more intelligible synthetic speech, and to improved automatic recognition. Toward this goal, a 111-word French paragraph was read by 29 native speakers from France. Measured durations of acoustic segments were significantly shorter than those in earlier studies of stressed words in French sentences read from a list. Previously recognized trends (short schwa vowels and function words; long unvoiced fricatives, nasalized vowels, and prepausal syllables) are confirmed and quantitative results are given. Vowels were longer preceding voiced fricatives (but not prior to /r/), and were also longer at sentence-internal pauses than at the end of a sentence. Standard deviations of acoustic segment durations (at fixed positions in the paragraph) across speakers averaged less than 25% in most cases. The exceptional, larger deviations occurred primarily in segments adjacent to pauses. Speaking rate variations could account for only one-sixth of the deviations, the rest being attributable to relatively free variation across speakers. A generative model of French durations, suitable for synthesis-by-rule, is presented, and applications to automatic recognition are discussed.
The detection of notes incompatible with scalar structure
Authors: Howell Peter , West Robert , Cross Ian
Published: October 2005

A fundamental question in the perception of melody is how listeners use pitch information to arrive at a sense of musical scale. We investigated possible ways in which this might be achieved. Listeners were required to detect notes incompatible with scalar structure in the course of melodic sequences. Within the parameters of our experimental sequences, the results showed that detection of nonscalar notes could be based on identifying nonscalar interval combinations (e.g., F♯, A, Bb), as well as by matching successive notes to a developing scalar schema. The strength of the scalar schema was influenced by relations between notes in the circle of fifths, with notes closer together in the circle of fifths (e.g., C, G, D, A) leading to a stronger schema than notes further apart (e.g., C, G, E, B).
Discrimination of the spatial distribution of concurrently active sound sources: Some experiments with stereophonic arrays
Authors: Perrott David R.
Published: October 2005

Several experiments are described in which subjects were required to discriminate differences in the spatial distribution of concurrently active sound sources in stereophonic arrays. For pure tone stimuli and binaural listening, systematic discrimination functions were observed when relatively small intersource frequency differences (approximately 30 Hz) were present. For tonal stimuli, this discrimination task was reliably performed only for frequencies below 1500 Hz. Additional tests were conducted with amplitude-modulated tonal stimuli, low- and high-frequency uncorrelated noise, correlated low-frequency noise, and, with the uncorrelated low-frequency noise, for stimuli presented in both the vertical plane and under monaural listening conditions. The results of all of these manipulations support the notion that the spatial distribution of sources in a stereophonic array can be appreciated if disparate low-frequency energy is available from the sources in a horizontal configuration. The implications of these results are discussed relative to acoustic processing in the natural environment.
Interaction of spontaneous oto-acoustic emissions and external sounds
Authors: Rabinowitz W. M. , Widin G. P.
Published: October 2005

Spontaneous oto-acoustic emissions (SOAEs) were detected in eight of 19 ears from 12 persons with normal hearing. On a subset of these individuals, additional characteristics of SOAEs were studied including the suppression of SOAE level caused by an external tone. For suppressor tones below and slightly above the frequency of an SOAE, suppression is quite abrupt (about 5 dB of SOAE level reduction per dB increase in suppressor level); however, as suppressor frequency increases above the SOAE, the rate of suppression decreases. A release from suppression was demonstrated by the interaction of an SOAE with two external tones. When a tone above the SOAE frequency causes suppression, a second tone above the suppressor frequency can cause the SOAE to increase nearly to its ambient level. This finding is interpreted as the second tone having suppressed some aspect of the intracochlear influence of the first tone. The growth rate of this secondary suppression appears to be near 1 dB/dB, a value similar to rates derived from existing measures of two-tone suppression observed in auditory-nerve-fiber recordings in laboratory mammals.
Spectral model and time-varying covariance functions for the nonstationary processes
Authors: Tsao Y. H.
Published: October 2005

A stochastic (random) process may be nonstationary if its stochastic features vary with a shift of time. For the most practical processes, although more or less nonstationary, the generalized harmonics representation still makes sense; so does the spectral density function which is now defined as being ‘‘evolutionary’’ in view of the time dependency. The present paper briefly reviews this spectral description for a nonstationary process and further models it as the output from a white-noise excited time-variant shaping filter. With this model the nonstationary processes X(t) and Y(t) are denoted as ∫∞−∞Ax,t(ω)ejωt dW(ω) and ∫∞−∞Ay,t(ω)ejωt dW(ω), respectively, where Ax,t(ω) and Ay,t(ω) are the so-called modulation functions (MFs) and dW(ω) is a random variable which retains the orthogonality. Previous papers have investigated and shown some advantage of using such a modulation function (MF) description in solving many practical nonstationary problems which hinged on the concept of the evolutionary auto/cross-spectral density (EASD/ECSD). In this paper an attempt is made to apply further this MF model to describe the time-varying auto/cross-covariance functions (ACVF/CCVF) for the nonstationary processes and it is found that they are closely related to the relevant MFs but not to the EASD/ECSD in the Fourier transform sense, as has been summarized in the well-known Wiener–Khintchine (W–K) relationship for the stationary processes. The new relationship has effectively generalized the W–K theorem in a special way, which has been proven efficient and accurate to both the synthetic signals such as the uniformly amplitude-modulated process, the uniformly frequency-modulated process and random-phase process, and to the practical signals such as the nonstationary acoustic processes.
Introduction of mass conservation law to improve the tomographic estimation of flow-velocity distribution from differential time-of-flight data
Authors: Sato Takuso , Aoki Hisayuki , Ikeda Osamu
Published: October 2005

The mass conservation law is combined as one of the utilizable physical constraints with differential time-of-flight data to improve the tomographic estimation of flow-velocity distribution by means of inverse operation of the matrix. The formulation and computer simulation are described.
Numerical calculation of flute impedances and standing waves
Authors: Strong William J. , Fletcher Neville H. , Silk Ron K.
Published: October 2005

The purpose of this study was to investigate a numerical method for calculating impedances and standing wave patterns of flute structures. To this end, the physical dimensions of flute joints and tone holes were used to compute impedance and standing waves as a function of frequency for several different fingerings. Numerically computed resonance frequencies for head joint, middle and foot joints, and complete flute are compared to experimentally measured values. Computed pressure standing wave patterns for two fingerings of A6 are compared to experimental values. Reasons for the observed discrepancies between the predicted and experimental frequencies are discussed.
Point source on the surface of a rigid, immobile sphere: Derivation of a useful equation
Authors: Egolf David P.
Published: October 2005

Reported herein is the derivation of an expression for sound pressure in the field of a point source of sound located on the surface of an otherwise rigid, immobile sphere. The derivation parallels those presented in several contemporary acoustics textbooks, but with the final equation given in terms of sound pressure: a useful quantity if one wishes to use such an equation to verify theory with actual sound-pressure measurements. Unfortunately, the authors of these textbooks have not seen fit to present the results of their work in this form. Proof of the validity of the equation derived herein is given by first reducing the expression to its farfield and low-frequency forms. These are then compared with similar forms of the equation which are, in fact, given in the referenced textbooks.
Nonlinear axisymmetric vibration of orthotropic thin annular plates with a rigid central mass
Authors: Dumir P. C. , Kumar Ch. R. , Gandhi M. L.
Published: October 2005

Large amplitude axisymmetric vibrations of uniform and tapered orthotropic annular plates with a rigid central mass are studied. A time-mode solution of the von Kármán-type-governing equations is obtained using the Kantorovich averaging method. The orthogonal point collocation method is used for spatial discretization. The effect of various parameters is studied.
Temporal summation by Pacinian corpuscles precludes entrainment at the detection threshold
Authors: Van Doren Clayton L.
Published: October 2005

For rapidly adapting mechanoreceptor afferents, entrainment is defined as a response of one spike per stimulus cycle. For Pacinian corpuscles, the entrainment threshold and psychophysical detection threshold are similar. The psychophysical threshold, however, exhibits temporal summation, which proves that the psychophysical threshold and the physiological entrainment threshold cannot be identical.
Audiovisual materials and microcomputer software for teaching vibration and sound
Authors: Stumpf F. B.
Published: October 2005

Currently available films, filmloops, slides, overhead transparencies, and microcomputer software are listed for those who teach courses involving vibration and sound. The topics covered and addresses of the suppliers are given.
Solution of the fundamental problem of transient acoustic propagation in a borehole with the hybrid method
Authors: Tsang Leung
Published: October 2005

The fundamental acoustic logging problem of a pulsed point source surrounded by both vertical and horizontal boundaries is solved with the hybrid method. The hybrid method yields the complete synthetic waveform including the head wave and the normal mode arrivals. The essence of the hybrid method consists in converting the head wave branch-cut contribution into discrete modes which, together with the normal modes, form a complete basis for the solution in each region. Boundary conditions at the horizontal bed boundary then couple the modes between different regions and enable the solution to be expressed in terms of reflection and transmission matrices of modes. Numerical results are illustrated as a function of the formation parameters. Transmission coefficients of head waves are calculated. The advantages of the hybrid method are also discussed.
Observations of sound propagation during a southern Alberta chinook
Authors: Bohlender David A. , Irwin Patrick J. , Mathews Titus
Published: October 2005

An experimental investigation of the propagation of sound in the presence of an elevated temperature inversion has been conducted on a farm site in southern Alberta. The refractive focusing of sound in the inversion layer was observed to cause shadow zones and regions of sound enhancement in which sound levels were up to 20 dB lower and 20 dB higher, respectively, than during normal afternoon conditions. Fluctuations of 35 dB in the sound intensities at microphones 1730 and 2180 m from the source have been witnessed as the location of the focusing region changed. Ray tracing analysis for meteorolgical data acquired predicts excess attenuations of sound consistent with those recorded. The use of a monostatic acoustic sounder proved useful in correlating anomalous sound levels with the appearance of temperature inversions.
Generalized Burgers equation for plane waves
Authors: Blackstock David T.
Published: October 2005

Burgers’ equation, an equation for plane waves of finite amplitude in thermoviscous fluids, is generalized by replacing the thermoviscous term Aut′t′ (A is the thermoviscous coefficient, u particle velocity, and t′ retarded time) with an operator L(u). This operator represents the effect of attenuation and dispersion, even if known only empirically. Specific forms of L(u) are given for thermoviscous fluids, relaxing fluids, and fluids for which viscous and thermal boundary layers are important. A method for specifying L(u) when the attenuation and dispersion properties are known only empirically is described. A perturbation solution of the generalized Burgers equation is carried out to third order. An example is discussed for the case α2=2α1, where α1 and α2 are the small-signal attenuation coefficients at the fundamental and second-harmonic frequencies, respectively. The growth/decay curve of the second harmonic component is given both with and without the inclusion of dispersion. Dispersion causes a small reduction of the component. The extension of the generalized Burgers equation to cover nonplanar one-dimensional waves is given.
A shallow water experiment to determine the source spectrum level of wind-generated noise
Authors: Kuperman W. A. , Ferla M. C.
Published: October 2005

An experiment was conducted in a shallow water region of the Mediterranean Sea to study wind-generated noise. In addition to measuring the noise field, propagation-loss data were collected and used in a detailed modeling of the environment. The environmental information was then used as input to a noise model based on wave theory that computes the noise field in the water column for a given (unknown) source strength. By comparing model predictions with data, the influence of the environment on recorded noise levels could be removed and a measure of the noise source spectrum levels obtained as a function of wind speed. It was found that noise levels correlate better with wind speed than with wave height. In addition it was found that the nearfield contribution dominates the noise level, with the result of producing virtually constant noise intensity over depth from moderate to high wind speeds and frequencies above 200 Hz.
The effect of signal degradation on the status of cues to voicing in utterance-final stop consonants
Authors: Wardrip-Fruin C.
Published: October 2005

In several recent studies, spectral acoustic cues (e.g., voicing during closure, preclosure transition) have been found to have more influence than temporal acoustic cues (e.g., vowel or syllable duration) on perception of the voicing distinction in final stops. Earlier studies, mostly using synthetic speech, had found vowel duration to be the primary cue to this distinction. The present stimuli were taken from a study in which spectral cues had dominated judgments in quiet listening conditions. These stimuli were presented against a high level of background noise (S/N=0) to seven normal adult subjects in a forced choice (e.g., BED–BET) format. In quiet, the correlation of the percentage of the original vowel remaining after deletion with judgments of the final stop as voiced had been 0.18. In the noise listening condition the correlation was 0.94. Syllables with voiced final stops from which 76% of the vowel (all but the final transition) had been deleted were judged voiced (82%) in quiet but voiceless (87%) in noise. These results indicate that the temporal cue of vowel duration is more resistant to degradation by noise than are spectral cues, and that vowel duration plays a dominant role only when other cues are unavailable.
Transduction principles of a liquid state electromagnetic transducer
Authors: Ajisaka Hidemi , Hixson Elmer L.
Published: October 2005

An electrically conductive fluid in a magnetic field generates forces by the application of an electric current in the fluid, and wave motion in the fluid generates an electromotive force. This effect is studied as an underwater acoustic transducer: liquid state electromagnetic transducer. For the two acoustic ports and the electrical port, three-port equations are derived, where the coefficients are functions of such physical parameters as the duct size, fluid conductance, wave speed in the duct, and magnetic flux density. Equivalent circuits are presented for the prediction of sensitivities, efficiencies, and other parameters.
Spectral domain formulation for acoustic radiation
Authors: Murphy Joseph E.
Published: October 2005

The farfield acoustic radiation amplitude of an arbitrary surface vibrating with specified periodic normal velocity is shown to satisfy an inhomogeneous integral equation similar to the quantum mechanical Lippmann–Schwinger equation.
Additional Comments on and Erratum for ‘‘Effect of finite ground impedance on the propagation of acoustic pulses’’ [J. Acoust. Soc. Am. 7
4, 267–274 (1983)]
Authors: Raspet Richard , Ezell Jean , Bass Henry E.
Published: October 2005

Results of an earlier paper [R. Raspet, H. E. Bass, and J. Ezell, J. Acoust. Soc. Am. 74, 267–274 (1983)] were based upon a computer code which was subsequently found to contain an error. The error affected some of the figures in the original paper and requires some modification of the conclusions. Using the corrected program, a careful study of surface wave effects on pulse propagation has been performed. Additional information about the pulse amplitude above a hard surface has been provided so that absolute magnitudes can be estimated from the calculations.
Finite-difference treatment of a time-domain parabolic equation: Theory
Authors: Murphy Joseph E.
Published: October 2005

A time-domain parabolic wave equation is derived from the usual acoustic wave equation used to describe underwater propagation. Using well-known finite-difference approximations, equations describing the pressure field within layers are derived. Discontinuities of sound speed and density at layer interfaces are properly accounted for by requiring continuity of pressure and particle velocity. The resulting tridiagonal systems of equations can be solved by standard methods.
A modification of the Galerkin method and the solution of the Helmholtz equation in regions of complicated boundary shape
Authors: Laura P. A. A. , Nava L. C. , Cortinez Victor Hugo , Laura Pablo Alejandro
Published: October 2005

An approximate approach proposed by R. Schmidt [J. Appl. Mech. 49, 639–640 (1982)] for optimizing the value of fundamental frequency coefficients when determined by variational methods in the case of one-dimensional problems is extended in the present letter in order to deal with domains of arbitrary shape, provided that the mapping function which maps the given shape onto a unit circle is known.
Applicability of the Biot theory. III. Wave speeds versus depth in marine sediments
Authors: Ogushwitz P. R.
Published: October 2005

Empirical and theoretical methods are used to estimate the elastic moduli of the skeletal frame in sedimentary materials. The Biot model is then used to estimate compressional wave speeds as a function of depth. These estimates are compared to laboratory data and to field measurements. Using the empirical method to estimate the frame moduli, the measured wave speeds are matched within 3% for Ottawa sand pack and within 10% for glass bead pack at pressures corresponding to depths of about 500 m or less. A new method for estimating the frame moduli of partially consolidated materials is used to quantify the effects of grain packing and cementation. Velocity gradients are estimated for shear and compressional waves in terrigenous sand and calcareous clay. Predicted gradients for compressional waves, when corrected for the effect of temperature, lie within the range of published values. Predicted gradients for shear waves fall within a range of shear-wave gradients determined from in situ measurements of saturated terrestrial and marine materials. Using a constant porosity of 0.40 to simulate conditions in pure sands, predicted compressional wave gradients agree with laboratory results.
Rough surface boundary wave attenuation due to incoherent scatter
Authors: Tolstoy I.
Published: October 2005

Calculation of the energy scattered out of an advancing wave front allows one to derive an attenuation coefficient δ for the low-frequency boundary mode carried by a rough interface between two media. For a point source of sound on or near the interface this leads to a farfield boundary wave pressure pB∝r−1/2f3/2e−δr with δ=Af6, where r is the range, f is the frequency, and A is a parameter which depends upon the form and size of roughness (for close packing it is proportional to the fifth power of the roughness height). For given r, then, pB must exhibit a maximum in the frequency domain at f=(4Ar)−1/6 and falls off sharply for higher frequencies. This paper gives a simple procedure for calculating A for bossy roughness models of two fluid interfaces. In the particular case of a hard rough boundary the theory predicts results in reasonable agreement with reported experimental results, at least insofar as the magnitude and shape of the pB(f) curve is concerned.
The influence of the physical properties of ice on reflectivity
Authors: McCammon Diana F. , McDaniel Suzanne T.
Published: October 2005

A model for the plane-wave reflection coefficient from a layered elastic solid bounded on either side by a fluid half-space is developed and applied to study environmental factors affecting the reflectivity of smooth arctic ice. Experimental measurements of the internal friction in ice and snow are reviewed and applied to compute realistic attenuation profiles. An examination of the effect of ice layers conforming with measured temperature profiles in floe ice shows that the use of average values for sound speed and attenuation is an acceptable approximation for modeling purposes. A study of the reflectivity due to the absorption of shear and compressional waves demonstrates that shear wave attenuation is the most important loss mechanism from 20° to 60° incidence. The effect of an additional snow layer is to produce more attenuation without shifting the pattern of reflection nulls. Major results are presented for a frequency of 2 kHz. Data comparisons are performed from 0.5–3 kHz that show a limited qualitative agreement with the model.
Sound amplification from controlled excitation reactions: Experimental observations in chemically reacting H2/Cl2 mixtures
Authors: Detsch Richard M. , Bass Henry E.
Published: October 2005

A study of sound propagation in chemically reacting mixtures has led to experimental observation of sound amplification. Photoinitiated Cl2–H2 reactions provided the energy for the amplification observed. Amplification experiments were conducted in two modes which were termed pulsed and cw. For the pulsed experiments, high-intensity UV flash lamps dissociated molecular chlorine at the start of the experiments and the Cl2–H2–Ar reactions quickly went to completion; amplification was observed for about 6 ms. The measured gain was 1.8 at 2 kHz compared to a gain of 4 predicted by theory. The source of this difference has not been resolved completely. In cw experiments, low-intensity UV fluorescent lamps dissociated molecular Cl2 continuously during the experiments, extending the time amplification was observed to about 800 ms. Experiments were conducted for three Cl2–H2–SF6 mixtures and four frequencies, 1.0, 2.5, 4.0, and 6.5 kHz. Computer calculations correctly predicted the frequency dependence of amplification and gave amplification values which were in fair agreement with the observations
Studies of parallel barrier performance by acoustical modeling
Authors: Hutchins D. A. , Jones H. W. , Paterson B. , Russell L. T.
Published: October 2005

An investigation is presented into the performance of parallel barrier configurations, using acoustical scale modeling. A realistic geometry is investigated, with the source being positioned over a paved roadway and the receiver over grass-covered ground. The grass-covered ground surface was properly modeled in terms of its impedance. Results were obtained for a range of barrier types, and demonstrate that frequency dependent effects are evident in barrier insertion loss data. In most cases, the barrier on the far side of the source did not significantly affect sound levels at the receiver. The most effective barrier design was found to be that of a gradual grass-covered slope up to an upright, thin barrier.
Super-resolution ultrasonic imaging by using adaptive focusing
Authors: Yokota Takayoshi , Sato Yakuso
Published: October 2005

In this paper, a new super-resolution ultrasonic imaging method is proposed. In this method, a set of reflected wave field data from an object is acquired by repeating the transmission and reception for all pairs of transducers on the array, then from these data the object-dependent adaptive focusing is performed in order to illuminate the desired points on the object at a constant level, and simultaneously, distributing nulls over the other regions of the object to suppress the signal. Image reconstruction is performed by scanning the adaptive focusing beam patterns over the object region and receiving the reflected wave field for this adaptive illumination. These procedures are carried out numerically by manipulating the acquired wave field data matrix and no actual beam scanning is required. Since the focusing is performed adaptively, the resolution of this method is much better than that of the extended two-dimensional maximum entropy method [Yokota and Sato, IEEE Trans. Acoust. Speech Signal Process. (April 1984)] and the active incoherent method [Yokota and Sato, Acoustical Imaging (Plenum, New York, 1982, Vol. 12; Yokota et al., J. Acoust. Soc. Am. (submitted)] for objects with fairly localized dominant reflecting regions. The effectiveness of the method is shown by numerical analysis and experimental results.
The possible role of the cochlear frequency-position map in auditory signal coding
Authors: Buchsbaum G.
Published: October 2005

The frequency-position map in the cochlea is considered as part of a signal decomposition mechanism whose purpose is redundancy reduction and information compression of auditory stimuli. A logarithmic-type frequency distribution is analytically derived from a heuristic model of the autocorrelation function of auditory signals and confronted with empirical data from the cat cochlea. It is argued that the logarithmic organization of frequency along the cochlea is designed to extract the maximum amount of information with the minimum number of hair cells.
The effects of cochlear hypothermia on compound action potential tuning
Authors: Shore Susan E. , Nuttall Alfred L.
Published: October 2005

The effects of lowered cochlear temperature on eighth-nerve tuning were assessed by using forward masking of whole nerve action potential (AP) responses to generate AP tuning curves (APTCs) at cochlear temperatures ranging from 38.5° to 30 °C for probe frequencies from 8 to 36 kHz. The data indicate that subnormal cochlear temperatures result in: (a) broadened APTCs for probe frequencies above 10 kHz which are interpreted as resulting from reduced hair-cell frequency selectivity, (b) lowered or more sensitive APTC tips where tone-burst thresholds are unchanged, and (c) raised or less sensitive tips where thresholds to tone bursts were elevated. Increased tip sensitivity is explained in terms of enhanced eighth-nerve adaptation which occurred during hypothermia. Experiments directly addressing adaptation were performed, in which the masker–probe interval (Δt) was systematically lengthened. The normalized AP decrement versus Δt functions indicate an enhancement of both the amount and duration of adaptation during hypothermia. Functions relating the growth of response to the masker (AP decrement versus masker intensity functions) were reduced at low temperatures.
Experiments on sound-absorbing Shaw-type horns with spatially varying effective density
Authors: Nagarkar B. N. , Finch R. D.
Published: October 2005

An experimental investigation of Shaw’s theory of sound propagation in acoustic horns with spatially varying density and elasticity is reported. The density-variation technique was used to simulate a conical horn in a tube of uniform cross section using perforated sheet metal plates. The performances of the density variation horn and the equivalent conical horn were evaluated by comparison of the acoustic impedance and the acoustic pressure within the horns. It was observed that the density-variation conical horn had sound-absorbing properties as a result of the use of the perforated plates. Due to the absorption properties of the density-variation cone it can be used as a muffler. A muffler was designed and its performance evaluated using both a loudspeaker and an internal combustion engine as sound sources.
Saturation of a nonlinear cylindrical sound wave generated by a sinusoidal source
Authors: Enflo B. O.
Published: October 2005

The propagation of a cylindrical sound wave generated by a sinusoidal source is studied in a nonlinear case by means of a generalized Burgers’ equation with two dimensionless parameters. The amplitude of the wave at a large distance from the source, where all higher harmonics are absorbed, is determined in a region for the two parameters where the amplitude is given by a single number not depending on the parameters. The method is to find a series expansion of the solution of the generalized Burgers’ equation. The series converges both far from the source and in the Taylor shock region nearer to the source. Despite the slow convergence of the series in the latter region it is possible to find the desired amplitude by means of an asymptotic expression for the terms in the series and some numerical work.