bluuebunny/crossref_metadata_2025 huggingface dataset:
The crevice model of bubble nucleation
Authors: Atchley Anthony A. , Prosperetti Andrea
Published: October 2005

The crevice model for heterogeneous nucleation of bubbles in water in response to a decreasing liquid pressure is studied. The model neglects gas-diffusion effects and is therefore more suited for acoustic than for flow cavitation. It is argued that previous work has overlooked the essential requirement of unstable growth of the interface in the crevice. As a consequence, the available results are incorrect in some cases. Another feature of the model which is considered is the process by which the interface moves out of the crevice. It is concluded that, depending on circumstances, the conditions for this step may be more stringent than those for the initial expansion of the nucleus inside the crevice. Some numerical examples are given to illustrate the complex behavior of nuclei, depending of geometrical parameters, gas saturation, contact angles, and other quantities.
A comprehensive model of wind-generated bubbles in the ocean and predictions of the effects on sound propagation at frequencies up to 40 kHz
Authors: Hall Marshall V.
Published: October 2005

A new expression is proposed for the population density spectrum of wind-generated bubbles in the sea based on measurements made by Johnson and Cooke [B. D. Johnson and R. C. Cooke, J. Geophys. Res. 84, 3761–3766 (1979)] and by Thorpe [S. A. Thorpe, Phil. Trans. R. Soc. London Ser. A 304, 155–210 (1982)]. The main departures from existing expressions are the narrowing of the radius spectrum with increasing depth and the conclusion from Thorpe’s data that the bubble density at the surface is proportional to the cube of the wind speed. For acoustic propagation at a given frequency, useful expressions for the resonant bubble radius, damping coefficient, the complex sound speed, attenuation, and the refraction spreading loss are presented. Predicted results for each of these parameters are calculated for frequencies of 0 Hz and from 1.25 to 40 kHz in octave steps. As frequency is increased, the dominant cause of loss changes from refraction to attenuation. For a wind speed of around 15 m/s, the transmission anomaly (attenuation plus refraction spreading losses) at high frequencies, for one-way horizontal transmission in the surface duct, is several bels if the source (or receiver) is adjacent to the actual sea surface, but falls to a few decibels if the transducer is 4 to 5 m below the surface. Results for the cumulative probability of transmission anomaly are shown for a typical case of vertical motion of an acoustic transducer. The accuracies of the more common approximations are also analyzed. The approximation that can cause the greatest error is that which ignores the (comparatively sharp) upward refraction of near-horizontal sound rays passing through the bubble layer, since the length of their path through the layer is significantly overestimated.
Bubble sources of the Knudsen sea noise spectra
Authors: Medwin Herman , Beaky Matthew M.
Published: October 2005

Single coherent bubble contributions to the incoherent underwater noise of spilling breakers have been studied in an anechoic laboratory facility. The waves are generated by a plunger, they propagate 17 m along a 1.2×1.2-m water waveguide, and ‘‘spill’’ and create bubbles at the surface of a 3×3×3-m anechoic cube of water. Several species of bubbles have been identified. In general, they act as transient dipoles of duration from 2 to several milliseconds, with peak axial source strength of the order of tenths of pascals, at 1 m. The noise is emitted when the bubble is within hundreds of micrometers or a few millimeters of the surface. Bubbles were observed in the 2 decades of frequency from 500 to 50 000 Hz. The average of the individual bubble events yielded a spectrum that slopes at about 5 dB/oct from 1 to 20 kHz, the same as the Knudsen wind noise spectra at sea. The magnitude of the laboratory breaker noise during continual wave-breaking events was approximately 80 dB re: 1 μ Pa2/Hz at 1 kHz, which is essentially the same as observed during the continual bubble production that occurs with very high winds at sea. The reasons for this agreement are discussed.
Complete period analysis of voiced sounds
Authors: Hao Shi , Puqiang Yan
Published: October 2005

In this paper, a complete period analysis (CPA) technique for analyzing voiced sounds in Chinese Putonghua is proposed. The concept of CPA technique is to block the voiced speech signal according to its period; that is, the length of each analysis frame is typically equal to one pitch period. The main advantages of CPA method are: (1) The spectrum variability due to analysis, especially when short time Fourier transform (STFT) is used, can be eliminated; (2) computation time can be saved considerably; and (3) accurate phase information can be obtained. To implement CPA, a special data acquisition system consisting of a real-time pitch extractor and a high-speed digital phase-locked loop (DPLL) has been developed, in which the sampling rate is adaptively adjusted according to the pitch period of the voiced sound signal to be sampled so that the number of points in each frame remains constant, and thus a fixed size discrete Fourier transform (DFT) can be applied. In this study, some experimental results are given, which show that CPA is especially suitable for Chinese Putonghua.
Range effects in the identification of lateral position
Authors: Koehnke J. , Durlach N. I.
Published: October 2005

Experiments on the identification of interaural time and interaural amplitude differences were conducted to evaluate the effects of stimulus range on identification performance. Three stimulus sets, large range (LR), small-range center (SRC), and small-range side (SRS), were used in experiments on interaural time and amplitude identification. As expected, data for both sets of measurements show worse resolution for LR than SRC or SRS, demonstrating that the ability to distinguish between two fixed interaural differences can be strongly influenced by the total range of such differences in the stimulus set.
Sound scattering by cylinders of finite length. III. Deformed cylinders
Authors: Stanton T. K.
Published: October 2005

A general solution is derived for the scattering of sound by cylinders of finite length with a deformed axis and composition profile and (cross-sectional) radius that vary along the axis. The orientation of the axis, plane-wave source direction, and point receiver position can also vary as long as the directions of incident and scattered fields are nearly perpendicular to the tangent of the axis (this restriction can be relaxed under some conditions). This approximate solution is a generalization of previous work [T. K. Stanton, J. Acoust. Soc. Am. 83, 55–63 (1988); and 83, 64–67 (1988)] where the scattering by straight finite cylinders of uniform fluid and elastic material, respectively, was described. In those articles, the volume flow per unit length of the scattered field of the cylinders was held constant along the length of the axis that restricted the axis to be straight and composition profile and (cross-sectional) radius to remain constant along the length of the axis. In this article, the volume flow per unit length is allowed to vary, thus allowing the above-mentioned quantities also to vary. As a result, an integral equation is derived that, in general, needs to be evaluated numerically. Examples are given in this article of the scattering of sound at all frequencies from a prolate spheroid with a high aspect ratio (i.e., high ratio of major axis to minor axis) and a uniformly bent finite cylinder of constant cross-sectional radius. There is excellent agreement between the (deformed cylinder) calculations involving the prolate spheroid and the exact spheroidal wave-function solution. Furthermore, numerical integration of the deformed cylinder formula required far less computer time than calculating the exact solution. Calculations involving the bent cylinder are compared to backscatter data from preserved euphausiids and suggest that the radius of curvature of the animals plays a major role in the acoustic scatter characteristics of the marine organisms. For example, at 200 kHz, the backscattering cross section of a 23-mm-long euphausiid will decrease by 6 dB if the animal bends by as little as 1.4 mm at the ends.
Instrumentation for i
n s
i
t
u acoustical measurements of bubble spectra under breaking waves
Authors: Breitz Nigel , Medwin Herman
Published: October 2005

A floating acoustical resonator has been developed to determine numbers and sizes of bubbles in the region of spilling breakers in the open sea. The change of Q of several modes of the one-dimensional resonator has been used to infer, simultaneously, bubble populations of nine radii between 30 and 270 μm; smaller radii bubbles can also be studied. To demonstrate the accuracy of the technique, theoretical predictions of resonance broadening due to bubbles were compared with measured broadening for a known bubble population in the laboratory. Statistics of bubble densities under and near spilling breakers were then obtained at a depth of 25 cm below the ocean surface. These ocean data compare very well with recently published laser measurements in a water–wind tunnel over radius range 30<a<270 μm, but agree with older photographically obtained values at sea only for radii 50<a<100 μm.
Transient generation of elastic waves in solids by a disk-shaped normal force source
Authors: Bresse L. F. , Hutchins D. A.
Published: October 2005

A method for computing the transient radiation from a wide circular source, acting at a solid surface, is given for two different normal force apodizations. This method, based on a double Laplace–Hankel transform and a Cagniard inversion, allows an exact formulation of the impulse response to be obtained for two components of the displacement at any point inside the solid and is amenable to computing the field for an arbitrary time excitation. Numerical results are presented and are compared with experimental results for generation by a piezoelectric transducer.
Vowel representation: Some observations on temporal and spectral properties of the first formant frequency
Authors: Di Benedetto Maria-Gabriella
Published: October 2005

Acoustic analysis of the vocalic portion of consonant–vowel–consonant (CVC) syllables (where V is one of the five vowels [I,q,1,a,v] of American English) spoken by three speakers (two males and one female) in the sentence frame ‘‘The — again’’ is presented. Results of acoustic measurements show that ambiguities between vowels, for each speaker, occur if the vowels are represented by the values of F1 and F2 sampled at the time where F1 reaches its maximum. These ambiguities occur primarily in the F1 dimension. Examination of the F1 trajectories of the vowels for which confusion occurs shows variations in the way F1 reaches its maximum among different vowels. In particular, if two different vowels such as [I] and [q] have the same maximum F1, then F1 for the lower vowel reaches its maximum value earlier. In addition, results show that the F1 onset frequency also might be important in determining vowel height. The implication is that the spectral characteristics at a particular ‘‘target,’’ represented by the time at which F1 reaches its maximum, are not invariant attributes of the vowel. The results support a hypothesis that time and/or frequency variations of the first formant must be taken into account if an invariant property is to be associated with a vowel.
Measurement of the bowing parameters in violin playing. II: Bow–bridge distance, dynamic range, and limits of bow force
Authors: Askenfelt Anders
Published: October 2005

A method is described that allows measurement of the bowing parameters in violin playing under normal conditions. The measured parameters include bow position, bow velocity, bow–bridge distance, and bow force. The use of the method is illustrated by registrations of typical bowing patterns (sustained notes, scales, crescendo–diminuendo, sforzando, and saltellato). The examples are analyzed with a focus on the players’ use of the bow–bridge distance and bow velocity in controlling the dynamic level. The correspondence between predicted and observed changes in the dynamic level is discussed, as well as the safety margins in bow force. The measurement method is a development of equipment earlier described [A. Askenfelt, J. Acoust. Soc. Am. 80. 1007–1015 (1986)].
A quasiarticulatory speech synthesizer for German language running in real time
Authors: Meyer Peter , Wilhelms Reiner , Strube Hans Werner
Published: October 2005

A system for simple quasiarticulatory speech synthesis is described. It is based on an articulatory model, which is controlled by seven parameters. The synthesizer employs a stylized vocal tract model that is realized using wave digital filter techniques. It includes a self-oscillating glottis model, voiceless excitation in the tract, damping, a nasal tract, and a radiation load that allows the simulation of lip protrusion. The synthesizer runs in real time on a signal processor. The described model was fit to natural speech using a Kalman filter algorithm. Simple rules for the synthesis of unrestricted German speech are described.
Segmental intelligibility of synthetic speech produced by rule
Authors: Logan John S. , Greene Beth G. , Pisoni David B.
Published: October 2005

This paper reports the results of an investigation that employed the modified rhyme test (MRT) to measure the segmental intelligibility of synthetic speech generated automatically by rule. Synthetic speech produced by ten text-to-speech systems was studied and compared to natural speech. A variation of the standard MRT was also used to study the effects of response set size on perceptual confusions. Results indicated that the segmental intelligibility scores formed a continuum. Several systems displayed very high levels of performance that were close to or equal to scores obtained with natural speech; other systems displayed substantially worse performance compared to natural speech. The overall performance of the best system, DECtalk—Paul, was equivalent to the data obtained with natural speech for consonants in syllable-initial position. The findings from this study are discussed in terms of the use of a set of standardized procedures for measuring intelligibility of synthetic speech under controlled laboratory conditions. Recent work investigating the perception of synthetic speech under more severe conditions in which greater demands are made on the listener’s processing resources is also considered. The wide range of intelligibility scores obtained in the present study demonstrates important differences in perception and suggests that not all synthetic speech is perceptually equivalent to the listener.
Discrimination of frequency transitions by human infants
Authors: Aslin Richard N.
Published: October 2005

Difference limens (DLs) for linear frequency transitions using a 1.0-kHz pulsed-tone standard were obtained from 6- to 9-month-old human infants in a series of three experiments. A repeating standard ‘‘yes–no’’ operant headturning technique and an adaptive staircase (tracking) procedure were used to obtain difference limens from a total of 71 infants. The DLs for 300-ms upward and downward linear frequency sweeps were approximately 3%–4% when the repeating standard was an unmodulated 1.0-kHz pulsed tone of 300-ms duration. These DLs for frequency sweeps were not significantly different from DLs for frequency increments and decrements using 330-ms pulsed tones [J. M. Sinnott and R. N. Aslin, J. Acoust. Soc. Am. 78, 1986–1992 (1985)]. The DLs for frequency sweeps of 50 ms appended to the beginning or the end of a 250-ms unmodulated 1.0-kHz tone were approximately 6%–7%. This greater DL for brief frequency sweeps was confirmed by varying the duration but not the extent of the sweep. Finally, DLs were greater than 50% when the repeating standard was a 50-ms rising or falling frequency sweep appended to the beginning of a 250-ms unmodulated 1.0-kHz tone. These results suggest that rapid frequency transitions are much more difficult to discriminate from frequency transitions of the same category (rising or falling) than from either a frequency transition of the opposite category (falling or rising) or an unmodulated tone. One implication of these results is that the categorical nature of infants’ or adults’ discrimination of stop consonants differing in place of articulation may originate in basic psychoacoustic limits on the discrimination of frequency transitions.
Indoor human response to blast sounds that generate rattles
Authors: Schomer Paul D. , Averbuch Aaron
Published: October 2005

The two major noise sources that cause environmental problems for the U. S. Army are helicopters and large weapons such as artillery, tanks, and demolition. These large weapons produce blast sounds that contain little energy above 200 Hz and that are particularly troublesome to deal with because they excite rattles in structures. The purpose of this study was to systematically test subjective response to the presence or absence of rattles in otherwise similar blast sound environments. A second purpose of the study was to test if there were structural changes that could reduce annoyance within the indoor blast sound environment. This study was done using a specially constructed test house and highly repeatable shake table to generate the blast sounds. The data clearly show that no commonly used environmental noise measure adequately describes the indoor environment when the blast excites rattles. Although the indoor blast ASEL changes by only about a decibel or so (and the indoor blast CSEL changes by even less), the subjective response changes by up to 13 dB. At low blast levels, the increase in human annoyance response is largest, and this annoyance response offset decreases to about 6 dB when the outside, flat-weighted peak sound-pressure level of the blast increases from 112 to 122 dB.
Broadband nearfield acoustical holography for vibrating cylinders
Authors: Williams Earl G. , Houston Brian H. , Bucaro Joseph A.
Published: October 2005

Generalized nearfield acoustical holography (GENAH), a noncontact technique to measure the vibration and radiation from vibrating cylinders, has been applied in the past to study submerged cylinders excited into vibration at a single frequency. The technique has been expanded to broadband excitation, so that from a single experiment several octaves of acoustic data can be provided. With this new capability GENAH reaches its full power as an experimental technique for studying the complete acoustics of a vibrating, fluid-loaded cylinder. GENAH is used to reconstruct the radial velocity on the surface of a capped cylinder driven into vibration with a miniature shaker. Important validation of this reconstruction is provided by an accelerometer attached to the surface, which is compared to the reconstructed velocity. Agreement between them over the band of measurement (2.0–8.0 kHz) is better than 2 dB.
Mode interference and mode filtering in shallow water: A comparison of acoustic measurements and modeling
Authors: Glattetre John , Knudsen Tor , So/strand Knut
Published: October 2005

This paper shows a successful modeling of some full-scale low-frequency acoustic measurements in shallow water. Match between model- and stable-measured Doppler spectra by means of an inverse-problem approach made estimation of geoacoustic and source parameters possible. Spatial coherence has been measured. Significant parts of the loss of spatial coherence are modeled and explained. A simple method has been formulated making it possible under certain conditions to estimate the spatial coherence function using a single hydrophone and a moving source. Finally, spatial mode filtering has been demonstrated using a horizontal array.
Ray treatment of wave propagation on thin-walled curved elastic plates with truncations
Authors: Felsen L. B. , Lu I. T.
Published: October 2005

Thin elastic plates form the building blocks in whole, or in part, for many structures of current interest. The acoustic response of such plates can be found from thin plate or shell equations. It has recently been shown (A. D. Pierce, IUTAM Meeting, Galway, Ireland, 1988) how time-harmonic point force excitation of a thin circular cylindrical elastic tube of uniform thickness and composition in vacuum can be modeled equivalently as line source excitation in a homogeneous anisotropic medium, and how the exact Fourier spectral integral representation of the field in the radiation zone can be reduced by asymptotics to distinct ray contributions that account for the anisotropy. For the cylindrical geometry, the thin shell equations yield three fundamental wave types established, at high frequencies, by compression, bending, and shear. By appealing to concepts of spectral localization, these results are extended here to allow for weak deviations brought about by variable radius of curvature, variations in thickness and(or) material properties, and edge truncations or joints. The treatment is approximate, based on localization of wave phenomena that occur at sufficiently high frequencies. Modifications for fluid loading have also been considered. The tools are adiabatic spectral transforms as well as uniform and nonuniform asymptotics with their ray or mode interpretations, as performed within the context of an equivalent inhomogeneous anisotropic medium with boundaries or interfaces. In essence, the aim of this study is to formulate for the acoustic response of a class of curved sections of thin plates a geometrical theory of diffraction.
Comments on ‘‘Spectrum factors relevant to phonetogram measurement’’ [J. Acoust. Soc. Am. 8
3, 2352–2360 (1988)]
Authors: Klingholz F.
Published: October 2005

In phonetograms, the contour of the forte sound-pressure level shows peaks and troughs. The question arises whether this structure is mainly determined by the F1/F0 ratio or could also be generated by register transitions.
A theoretical study of cavitation generated by an extracorporeal shock wave lithotripter
Authors: Church Charles C.
Published: October 2005

The intense acoustic wave generated at the focus of an extracorporeal shock wave lithotripter is modeled as the impulse response of a parallel RLC circuit. The shock wave consists of a zero rise time positive spike that falls to 0 at 1 μs followed by a negative pressure component 6 μs long with amplitudes scaled to +1000 and −160 bars, P+ and P−, respectively. This pressure wave drives the Gilmore–Akulichev formulation for bubble dynamics; the zero-order effect of gas diffusion on bubble response is included. The negative pressure component of a 1000-bar shock wave will cause a preexisting bubble in the 1- to 10-μm range to expand to over 100 times its initial size, R0, for 250 μs, with a peak radius of ∼1400 μm, then collapse very violently, emitting far UV or soft x-ray photons (black body). Gas diffusion does not appreciably mitigate the amplitude of the pressure wave radiated at the primary collapse, but does significantly reduce the collapse temperature. Diffusion also increases the bubble radius from R0 up to 40 μm and extends the duration of ringing following the primary collapse, assuming that the bubble does not break up or shed microbubbles. Results are sensitive to P+/P− and to the duration of the negative pressure cycle but not to rise time.
Comparison of discomfort levels obtained with pure tones and multitone complexes
Authors: Bentler Ruth A. , Pavlovic Chaslav V.
Published: October 2005

The relationship between threshold of discomfort (TD) estimates and the number of components in a complex signal has been investigated. The thresholds of discomfort were first obtained for 16 pure tones located at the center frequency of critical bands from 250 to 4000 Hz. Subsequently, thresholds of discomfort were obtained for 2, 4, 8, and 16 tone complexes. The pure-tone components of the complexes were systematically selected from the same 16 pure tones. For each subject, the relative intensities of the components in the four complexes were determined in such a way so as to parallel the pure tone TD contour obtained for that subject. Data were obtained from 15 normal and 15 hearing impaired adults. The individuals in the latter group all had mild to moderate sensorineural hearing loss. Summation of discomfort (S) was defined as the difference between the threshold of discomfort for a pure tone presented in isolation and within the complex. The two groups demonstrated different summation values. For both groups, however, the summation was shown to be a linear function of the logarithm of the number of components in the complex: S=a+b log (n) where n is the number of components (2, 4, 8, 16). For the normal hearing group, a and b are 2.05 and 11.51, respectively, while for the hearing impaired group, they are 3.95 and 12.88, respectively. While the future digital hearing aids can easily regulate their limiting levels so as to accurately account for this summation, present day hearing aids may underestimate this effect. However, given current clinical practices (which somewhat underestimate the pure-tone TD) this is probably not the case.
Dynamic spectral transforms: Properties of the canted spectral transform
Authors: Gerlach Albert A. , Flowers Kenneth D. , Anderson Wendell L. , Kunz Edward L.
Published: October 2005

A generalized spectral transform is defined by extending the kernel of the conventional sectionalized Fourier transform (SFT). The generalized transform accumulates signal energy along narrow dynamic spectral channels that may be made to conform to the instantaneous-frequency dynamics of a given signal. This property may be used to achieve optimum detection of a deterministically known signal or to estimate the spectral dynamics of an unknown signal over the temporal limits of the transform. As an initial step toward achieving the spectral transform, the canted spectral transform (CST) is defined by using a quadratic phase kernel. The statistical properties of the CST are derived and compared with those of the conventional SFT. In general, the use of shaded windows in the CST does not appear to be advantageous and can degrade the selectivity of the transform in estimating the signal frequency dynamics. Statistical distributions of the peak cant variable for an idealized signal in Gaussian noise provide a basis for determining the performance of the CST in practical applications.
A new autoregressive method for high-performance spectrum analysis
Authors: Lee An-Chen
Published: October 2005

In this paper, a new method of autoregressive (AR) spectrum estimation is presented. It shall be called two-sided autoregressive spectrum estimation, because an interpolative or smoothing model is postulated, as opposed to the predictive (one-sided) model used in AR modeling. The matrix equations arising in the estimation procedures proposed in this paper exhibit a special structure. The exploitation of these structures leads to fast solutions that reduce the total number of computations by an order of magnitude compared with straightforward approaches. Also, special attention is directed to the constrained two-sided AR model. Simulation examples show higher resolution capability of the proposed method relative to the least-squares AR method.
Extended towed array processing by an overlap correlator
Authors: Stergiopoulos Stergios , Sullivan Edmund J.
Published: October 2005

A method of extending towed array measurements that provides an aperture greater than that of the physical array is presented. Such a technique can be used by matched-field estimators to obtain information about the range and depth of a source and in other towed array applications requiring a very large aperture. The approach is to combine coherently the acoustic signals arriving at a moving array of hydrophones by making proper compensation through a factor that corrects for considerable fluctuations in phase irregularities in the tow path of the physical array as well as fluctuations in amplitude experienced during the coherent integration time. In this manner, the finite aperture of the physical array is exploited in a process that synthesizes the extended aperture of the method. The concept is based on an algorithm that we call an ‘‘overlap correlator,’’ which provides the phase correction factor by correlating overlapping space samples of the acoustic signal received at successive moments by the moving towed array. This is in contrast to the standard, passive synthetic aperture technique, which requires either highly accurate a priori knowledge of the source frequency or a maneuver in order to obtain a wavenumber or bearing estimate. The algorithm has been tested on numerical data generated by the SACLANT Undersea Research Centre’s normal mode model SNAP. The effects of space and time coherence of the signal and the random and systematic errors on the extended towed array measurements are examined and used to derive guidelines for experimental applications of this algorithm.
Simulation of the transient and steady-state sound propagation in rooms using a new combined ray-tracing/image-source algorithm
Authors: Vorländer Michael
Published: October 2005

A new method for the calculation of room acoustical impulse responses is described, which is based on two well-known computer algorithms, the ray-tracing and the image-source models. With the new method, the procedure of sieving the ‘‘visible’’ image sources out of the enormous quantity of possible sources is carried out by examination of the histories of sound particles. From the obtained list of visible image sources, the impulse response of the enclosure is easily constructed. The new method combines the advantages of the ray-tracing process, namely, the relatively slow increase of computation time with the length of the impulse response, with the accuracy inherent to the image-source model, which is even sufficient to calculate the Fourier transform, i.e., the steady-state transmission function of the room, or to convolve the impulse response with sound signals.
Parabolic-equation modeling with angle-dependent surface loss
Authors: Moore-Head M. E. , Jobst W. , Holmes Eleanor S.
Published: October 2005

This paper presents a method for using surface loss as a function of angle in a parabolic-equation (PE) model. In this method, the complex pressure field in a layer near the surface is transformed to vertical wavenumber space where a loss function is applied. The field is then transformed back to depth space and merged with the field outside the layer in preparation for the next range step in the PE model. Test cases show the method to be computationally efficient as well as accurate.
Lamb waves and fluid-borne waves on water-loaded, air-filled thin spherical shells
Authors: Talmant Maryline , Überall H. , Miller Russel D. , Werby Michael F. , Dickey J. W.
Published: October 2005

The results of a recent study of fluid-borne waves on plates with one-sided fluid loading [M. Talmant, Ph.D. thesis, University of Paris VII (1987)] allow the prediction of the corresponding waves and their resonances (as well as of the Lamb-wave resonances) on thin submerged spherical shells. Similar fluid waves and the ensuing ‘‘bifurcation’’ in the dispersion curves of the first antisymmetric vibration mode on cylindrical shells were previously described [J. V. Subrahmanyam, Ph.D. thesis, Catholic University of America (1983); J. L. Rousselot, Acustica 58, 291 (1985)] and the fluid waves were observed by Talmant et al. [J. Acoust. Soc. Am. 84, 681–688 (1988)]. The resonances predicted by the plate model for spherical shells are confirmed here by comparison with scattering cross-section calculations using surface integral equation radiation and scattering (SIERRAS) and T-matrix codes.
Ultrasonic reflection mode imaging of the nonlinear parameter B/A. II: Signal processing
Authors: Cain Charles A. , Houshmand Hooman
Published: October 2005

The nonlinear acoustic interaction between a reflected single-frequency sinusoid and a broadband pump waveform propagating in the opposite direction produces phase changes in the probe proportional to the nonlinear parameter B/A in the spatial region of interaction. The instantaneous phase change along the received probe can be expressed as the convolution of the pump waveform with the spatial distribution of B/A along the propagation path over which the pump and reflected probe interact. In theory, the phase modulated sinusoidal probe can be processed (phase detection and deconvolution) to produce an ‘‘A-mode’’ representation of B/A. If the pump is an intense unipolar impulse and the probe a swept-frequency sinusoid, then the pump interacts with the probe at each point along the propagation path at a unique frequency. Thus the phase modulation that carries information about the spatial distribution of B/A can be extracted from the phase spectrum by a simple Fourier transformation analogous to the space to frequency mapping so basic to magnetic resonance imaging. If the impulsive pump is replaced by another swept-frequency sinusoid, then the phase change in the probe due to B/A at a particular point along the propagation path will be spread out for the duration of the pump along the probe. Passage of the received signal through an appropriate matched filter restores spatial coherence to the phase information in the probe so that it can be processed as if the pump were a broadbanded impulse. This approach suggests a means of approaching the design of effective pump waveforms that can resolve a wide range of spatial frequencies in (B/A)(x).
Estimation of sea surface spectra using acoustic tomography
Authors: Miller James H. , Lynch James F. , Chiu Ching-Sang
Published: October 2005

Ocean acoustic tomography signals that interact with the ocean surface suffer travel time perturbations which have information on the frequency-direction spectrum of that surface. In this paper, a technique for tomographically estimating spatially varying frequency-direction spectra is introduced. To demonstrate this technique, synthetic signal spectra data were generated using an empirical model for a fetch-limited sea. The synthetic data were then inverted using linear inverse techniques to produce an estimate of the original sea surface spectra. Inverse solutions for both noise-free and noisy experiments are presented and discussed.
Observations of low-frequency acoustic-to-seismic coupling in the summer and winter
Authors: Albert Donald G. , Orcutt John A.
Published: October 2005

Experiments were conducted at a site in northern Vermont to investigate low-energy acoustic-to-seismic coupling in the 5- to 500-Hz frequency band for propagation distances between 1 and 274 m. Pistol shots were used as the source of the acoustic waves, with geophones and microphones serving as the receivers. The strongest coupling into the ground occurred as the air wave passed, with measured ratios of about 7 and 6×10−6 m s−1 Pa−1 in the summer and winter, respectively. Compressional waves induced in the ground immediately under the source were observed as first arrivals, since they travel at the higher subsurface seismic wave velocity, but their amplitudes were one to two orders of magnitude lower than those of the later-arriving air wave. A comparison of the summer and winter recordings revealed a number of effects caused by the introduction of a 0.25-m-thick snow cover. The peak amplitude of the seismic arrival induced by the passage of the acoustic wave was more strongly attenuated in the winter, with a decay rate proportional to r−1.9 vs r−1.2 in the summer. These observed decay rates are shown to agree with the calculated absorption of energy from the airborne acoustic wave by the finite impedance ground surface. The snow cover also produced a strong waveguide effect that enhanced the low-frequency air-coupled Rayleigh waves and considerably changed the appearance of the received waveforms.
Measurements of ambient seabed seismic levels below 1.0 Hz on the shallow eastern U.S. continental shelf
Authors: Trevorrow Mark V. , Yamamoto Tokuo , Turgut Altan , Goodman Dean
Published: October 2005

Measurements of ambient seismic noise levels in the range 0.03–1.0 Hz were made using ocean-bottom seismometers (OBS) at four shallow-water (<100 m) locations on the New Jersey Shelf and George’s Bank. Surface gravity-wave-induced seabed motion (single-frequency microseism) was found to be dominant in the frequency range 0.03–0.3 Hz, with the high-frequency cutoff strongly dependent on water depth. The peak seismic level in the water wave band was measured at 2.0×10−8 (m/s2)2/Hz in 12 m of water. This level was observed to decrease rapidly with greater water depth. Seismic interface waves (microseisms) of power level approximately 5×10−10 (m/s2)2/Hz were observed in the range 0.25–1.0 Hz. This microseism power level was found to be roughly constant in water depths from 12 to 70 m. A quiet ‘‘notch’’ between the two wave bands, in the range 0.15–0.3 Hz, was observed. The background seismic level in this notch was determined to be less than 5×10−12 (m/s2)2/Hz. Extrapolations of the observed pressures and seabed motions into deeper water conditions are made.
Effects of bubbly layers on wave propagation
Authors: Miksis Michael J. , Ting Lu
Published: October 2005

The transmission and reflection of an acoustic wave through a bubbly layer are investigated. Nonlinear model equations for the bubbly liquid are used. These equations first linearized and solved exactly for a time-harmonic incident wave. Then, numerical solutions of the nonlinear system are found. It is found that even for a small amplitude incident pressure wave, it is possible to have nonlinear transmitted and reflected waves. The limit where the bubbly layer is thin relative to the incident wavelength is also considered. By using the method of matched asymptotic expansions, it is found that the bubbly layer can be replaced by an interface subject to the continuity of pressure and an effective nonlinear jump condition. The latter involves the internal effects of the layer. Solutions of this limiting case are compared with the numerical results and good agreement is found even when the ratio of the bubbly layer thickness to the incident wavelength is of order 1.
Floquet wave properties in a periodically layered medium
Authors: Rousseau M.
Published: October 2005

In a periodically stratified medium, the acoustic propagation for wavelength of the order of the period is conveniently described by Floquet waves. A first part of this paper is concerned with a fluid medium and it completes previous results showing the existence of a pseudocritical angle. The extension to an elastic medium allows the introduction of the shear effects inside the layers. Several properties of Floquet waves are exhibited; the particular case of a medium composed of fluid and solid layers is also studied.
Acoustic multipole logging in transversely isotropic poroelastic formations
Authors: Schmitt Denis P.
Published: October 2005

The properties of the modes generated by multipole sources in a fluid-filled borehole embedded in (radially layered) formations that include transversely isotropic poroelastic layers are investigated. These layers are modeled following Biot’s and homogenization theories, under the assumption that the principal axes of symmetry of both the transversely isotropic skeleton and the complex permeability tensor are parallel to the vertical axis of the borehole. A general formulation based on the Thomson–Haskell method accounts for any combination of fluid, elastic, and poroelastic layers, either isotropic or transversely isotropic. The investigation is achieved through the computation of dispersion and attenuation curves, and frequency-dependent sensitivity coefficients with respect to the parameters. In the presence of a fast or slow radially semi-infinite transversely isotropic poroelastic formation with an impermeable borehole wall, the shear-wave transverse isotropy of the skeleton can be determined using the low-frequency parts of the fundamental modes generated by a monopole source and one of higher order. With a permeable interface, the fluid flow effects refer to the horizontal mobility (horizontal permeability/saturant fluid viscosity) and disables the determination of the shear-wave transverse isotropy. Without this information, any horizontal mobility determination is incorrect. Whatever the nature of any fluid–poroelastic interface, the presence of radial layering decreases the reliability of any estimation of parameter related to the virgin formation except for the velocity and attenuation of the vertically propagating SV wave. Whatever the configuration, the transverse isotropy of the compressional wave velocity cannot be determined nor can that of the complex permeability tensor or the anelastic attenuation due to the polarization of the (quasi) body waves involved. The results of this work also show that, in contrast to the pure elastic situation, a transverse isotropy of the complex permeability tensor leads to slightly different quasi-SV-wave velocities along the principal directions of propagation at ultrasonic frequencies.
Method for computing spatial pulse response: Time-domain approach
Authors: Piwakowski B. , Delannoy B.
Published: October 2005

The computer-aided, time-domain method is a proposal to determine the spatial pulse response for an arbitrarily shaped source and for arbitrary aperture velocity and delay distributions. The computational procedure ‘‘generates’’ the pulse response function by directly repeating the physical stages that accompany the creation of this phenomenon, such as radiation from the surface element, and propagation and summation in the observation point. The method is very simple mathematically, employing a simple algorithm, and can be easily implemented—even on a small minicomputer. The mathematical work required prior to the computation has been greatly simplified; the commonly studied behavior of the derivatives (arrival time/source point), as well as the exact temporal limits of the pulse response occurrence, need not be analyzed. The Dirac-type free-space Green’s function, as well as other arbitrary types of the causal Green’s function, can also be considered. The obtainable results are approximate, but computational precision depends only on the number of the elementary surfaces used to model the aperture, and, therefore, can be obtained practically, as desired. The method can also be easily used for computations of the transducer coupling functions and of the transient field diffracted by an arbitrary object. The nonplanar sources and objects can also be considered.
Determining the extent of coarticulation: Effects of experimental design
Authors: Gelfer Carole E. , Bell-Berti Fredericka , Harris Katherine S.
Published: October 2005

The purpose of this letter is to explore some reasons for what appear to be conflicting reports regarding the nature and extent of anticipatory coarticulation, in general, and anticipatory lip rounding, in particular. Analyses of labial electromyographic and kinematic data using a minimal-pair paradigm allowed for the differentiation of consonantal and vocalic effects, supporting a frame versus a feature-spreading model of coarticulation. It is believed that the apparent conflicts of previous studies of anticipatory coarticulation might be resolved if experimental design made more use of contrastive minimal pairs and relied less on assumptions about feature specifications of phones.
Noise and vibration interactions: Effects on hearing
Authors: Hamernik Roger P. , Ahroon William A. , Davis Robert I. , Axelsson Alf
Published: October 2005

There is the suggestion in the literature that vibration may potentiate the effects of noise and may thus increase the risk of hearing loss in a variety of exposure situations. However, in human experimental studies, which, by necessity, are limited to low levels of exposure, the effects measured are relatively small. A very limited number of animal studies have also shown an enhanced noise-induced hearing loss in the presence of vibration, but the scope of these studies is limited. The animal studies (chinchilla) that form the basis of this report were performed using a 30-Hz, 3g rms and a 20-Hz, 1.3g rms cage vibration separately and in combination with continuous noise (95-dB, 0.5-kHz octave band) and impact noise (113, 119, or 125 dB peak SPL) exposure paradigms. All exposures lasted for 5 days. The impact noise exposures were designed to have approximately equal total energy. Temporary and permanent threshold shifts were measured using evoked potentials, and sensory cell loss was measured using surface preparation histology. The results obtained from some of the noise/vibration paradigms showed that such exposures can alter some of the dependent measures of hearing. This effect was statistically significant only for the stronger vibration exposure conditions and was evident primarily in the extent of the outer hair cell losses and in the shape of the PTS audiogram.
Modulation interference in detection and discrimination of amplitude modulation
Authors: Yost William A. , Sheft Stanley , Opie Janie
Published: October 2005

Two experiments were conducted to assess the effect of the rate of sinusoidal amplitude modulation (SAM) of a masker tone on detection of SAM of a probe tone (experiment 1) or on SAM-rate discrimination for the probe tone (experiment 2). When modulated at the same rate as the probe, the masker interfered with both the detection of probe modulation and the discrimination of the rate of probe modulation. The interference was obtained when the masker was either higher or lower in frequency than the probe (the probe and masker were separated by 2 oct). The amount of interference in detecting probe modulation (experiment 1) decreased as the common base rate of modulation was increased from 5 to 200 Hz. For rate discrimination (experiment 2), the amount of interference remained approximately the same for base rates of 2–40 Hz, the range over which rate discrimination was measured. In both experiments, the amount of interference was reduced when the masker was modulated at a different rate than the probe.
Segregation of concurrent sounds. I: Effects of frequency modulation coherence
Authors: McAdams Stephen
Published: October 2005

Frequency modulation coherence was investigated as a possible cue for the perceptual segregation of concurrent sound sources. Synthesized chords of 2-s duration and comprising six permutations of three sung vowels (/a/, /i/, /o/) at three fundamental frequencies (130.8, 174.6, and 233.1 Hz) were constructed. In one condition, no vowels were modulated, and, in a second, all three were modulated coherently such that the ratio relations among all frequency components were maintained. In a third group of conditions, one vowel was modulated, while the other two remained steady. In a fourth group, one vowel was modulated independently of the two other vowels, which were modulated coherently with one another. Subjects were asked to judge the perceived prominence of each of the three vowels in each chord. Judged prominence increased significantly when the target vowel was modulated compared to when it was not, with the greatest increase being found for higher fundamental frequencies. The increase in prominence with modulation was unaffected by whether the target was modulated coherently or not with nontarget vowels. The modulation and pitch position of nontarget vowels had no effect on target vowel prominence. These results are discussed in terms of possible concurrent auditory grouping principles.