bluuebunny/crossref_metadata_2025 huggingface dataset:
Active control of far-field sound radiated by a rectangular panel—A general analysis
Authors: Pan Jie , Snyder Scott D. , Hansen Colin H. , Fuller Christopher R.
Published: October 2005

In this paper a general analysis is presented for the active control of the far-field harmonic sound radiated by a rectangular panel that is built into an infinite baffle. In this analysis, the panel vibration may be generated by either airborne sound (incident sound field) or by structure borne vibrations. The far-field radiated sound is controlled either by acoustical sources or vibration sources. Minimization of both the local sound pressure and the total power output is considered. Analytical results for the particular case involving minimization of the sound pressure at a single point are compared with experimental data. The physical mechanisms involved for different control sources (vibration or acoustic) are demonstrated analytically. For the case of vibration control sources, the panel modal velocity components are adjusted to produce far-field sound control. This can be done either by decreasing their amplitudes, and/or by changing the temporal phases of the panel modes. However, for acoustic control sources, the far-field sound is minimized by alteration of the radiation impedance seen by the vibrating panel and the control sources.
Symmetrization of random data via random thresholding
Authors: Li Xiaojun , Morris Joel M.
Published: October 2005

A method by which asymmetrical random data can be transformed to equivalent symmetrical or approximately symmetrical data is presented. The symmetrization operation is based on the concept of random thresholding. Information about the probability density or central moments, at least the third-order central moment, is needed to define the constrained optimization problem that specifies the random threshold variable for accomplishing the symmetrization. An example of an application to detection is presented.
On the degree of rigidity of the manubrium in a finite-element model of the cat eardrum
Authors: Funnell W. Robert J. , Khanna Shyam M. , Decraemer Willem F.
Published: October 2005

It has always been assumed that the manubrium is in effect perfectly rigid. In this paper, a more realistic model of the manubrium is incorporated into an existing finite-element model of the cat eardrum. The manubrial thickness is based on a three-dimensional reconstruction from serial histological sections. After a review of the literature, a value of 2×1011 dyn cm−2 is adopted for the Young’s modulus of the bone. The mode of vibration of the model is investigated for different manubrial-thickness values and it is found that a significant degree of manubrial bending occurs in the model for realistic values of manubrial thickness. As a result of the bending, the frequency response at the umbo at high frequencies displays much higher amplitudes and larger phase lags than when the manubrium is rigid. The bending will also affect the displacements transmitted to the ossicular load, and introduce significant errors into estimates of such displacements based on measurements of umbo displacement even at frequencies as low as a few kHz. Recent measurements of manubrium vibrations in the cat ear provide experimental evidence of bending.
A computer model of a cochlear-nucleus stellate cell: Responses to amplitude-modulated and pure-tone stimuli
Authors: Hewitt Michael J. , Meddis Ray , Shackleton Trevor M.
Published: October 2005

A computer model of a ventral-cochlear-nucleus (VCN) stellate cell with chop-S type response properties is presented and evaluated. The model is based on a simplified model of spike generation preceded by a stage that simulates dendritic low-pass filtering. Input to the model is in the form of simulated auditory-nerve spikes produced by a model of the auditory periphery [Meddis and Hewitt, J. Acoust. Soc. Am. 89, 2866–2882 (1991)]. Outputs from the stellate-cell model are shown to qualitatively replicate a wide range of typical in vivo responses. These include: (a) realistic onset and steady-state rate-level functions, (b) ‘‘chopper’’-type post-stimulus time histogram responses; (c) typical ‘‘chop-S’’-type neuron responses characterized by a low coefficient of variance (CV<0.3) of interspike intervals as a function of time; (d) level-dependent amplitude-modulation transfer functions; (e) intrinsic oscillations in responses to pure-tone stimuli; (f) amplitude-modulation encoding over a wide dynamic range; and (g) frequency-limited phase locking to pure tones. It is shown that these responses can be explained primarily by the membrane properties of the cells. More specifically, how the model encodes signal amplitude modulation was studied and an explanation was suggested for the generation of the bandpass modulation transfer functions. Such functions are observed neurally in response to amplitude-modulated stimuli presented at moderate to high signal levels.
A computationally efficient representation for propagation of elastic waves in anisotropic solids
Authors: Tewary V. K. , Fortunko C. M.
Published: October 2005

A new closed-form representation is developed for the exact solution of the Christoffel equation for wave propagation in solids. The new representation is numerically more efficient than the traditional representations based on the use of Fourier and Laplace transforms. Using the new representation, the retarded Green’s functions are derived for an infinite anisotropic solid and an anisotropic half-space. The method is applied to calculate the elastic-wave response of an anisotropic cubic solid to highly localized delta function and step function type impulses. Both surface and bulk wave responses have been calculated. The effect of anisotropy is discussed by considering cubic solids with different anisotropy parameters. Interestingly, it is found that, for certain values of the anisotropy parameter, two distinct longitudinally polarized components can be observed to propagate along an axis of cubic symmetry. One of the signals is the normal longitudinal wave signal while the other results from the concave shape of the transverse slowness surface.
Acoustically forced oscillations of air bubbles in water: Experimental results
Authors: Holt R. Glynn , Crum Lawrence A.
Published: October 2005

An experimental technique for measuring the time-varying response of an oscillating, acoustically levitated air bubble in water is developed. The bubble is levitated in a resonant cell driven in the (r,θ,z) mode of (1,0,1) at a frequency fd≊24 kHz. Linearly polarized laser light (Ar–I 488.0 nm) is scattered from the bubble, and the scattered intensity is measured with a suitable photodetector positioned at some known angle from the forward, subtending some solid acceptance angle. The output photodetector current, which is linearly proportional to the light intensity, is converted into a voltage, digitized, and then stored on a computer for analysis. For spherical bubbles, the scattered intensity Iexp(t) as a function of radius R and angle θ is calculated theoretically by solving the boundary value problem (Mie theory) for the water/bubble interface. The inverse transfer function R(I) is obtained by integrating over the solid angle centered at some constant θ. Using R(I) as a look-up table, the radius versus time [R(t)] response is calculated from the measured intensity versus time [Iexp(R,t)]. Fourier and phase space analyses are applied to individual R(t) curves. Resonance response curves are also constructed from the R(t) curves for equilibrium radii ranging from 20 to 90 microns, and harmonic resonances are observed. Comparisons are made to a model for bubble oscillations developed by Prosperetti et al. [Prosperetti et al., J. Acoust. Soc. Am. 83, 502 (1988)]. Complex Iexp(t) behavior is also measured, with subharmonics and broadband noise apparent in the Fourier spectra. Possible explanations for this phenomenon are discussed, including shape oscillations and chaos.
A method to overcome computational difficulties in the exterior acoustics problem
Authors: Segalman D. J. , Lobitz D. W.
Published: October 2005

When the boundary integral equation method is applied to exterior acoustics problems, singularities occur in the resulting algebraic equations at various frequencies associated with the eigenvalues of an interior problem. These frequencies are referred to as ‘‘forbidden,’’ and various methods have been devised to overcome the computational difficulties presented at these frequencies. The work presented here is an extension to the CHIEF method in that higher derivatives, in addition to the function itself, are constrained to be zero at selected points in the interior domain. Whereas the relative success of either method depends on the quantity and selection of interior points, the SuperCHIEF method requires fewer interior points and is less sensitive to point selection, resulting in improved robustness without a significant increase in computational complexity.
Sound propagation over a surface with varying impedance: A parabolic equation approach
Authors: Craddock James N. , White Michael J.
Published: October 2005

This paper describes modifications to a finite element solution for the wide angle parabolic equation (PE). The modifications to the PE allow the computationally efficient solution of the problem of sound propagation over ground whose impedance varies with range. In particular, the set of linear algebraic equations that propagate the field outward in range is solved with a UL (upper, lower triangular) decomposition, instead of the standard LU (lower, upper triangular) scheme. This approach allows the change in impedance to affect only a single element in the decomposition. Consequently, all previous calculations in the decomposition can be saved in proceeding from one range step to the next. Results are presented for several cases, in which the ground suffers an abrupt change in acoustic impedance at some distance along the propagation path. Comparisons to existing experimental data are made and the method presented here matches the published data quite well. Other diffraction cases are presented for which no experimental data are available, however the results are fairly self-consistent and serve to indicate the versatility of this method. The approach described in this paper represents an accurate and efficient method for solving problems involving sound propagation over ground having a range-dependent surface impedance.
The role of envelope fluctuations in an apparent demonstration of suppression in simultaneous masking
Authors: Wright Beverly A.
Published: October 2005

Fastl and Bechly [J. Acoust. Soc. Am. 74, 754–757 (1983)] reported that the threshold of a brief 900-Hz signal simultaneously masked by a band of noise, 100 Hz wide, centered at 1000 Hz, was reduced by approximately 8 dB by the addition of an 1150-Hz tone having a level of 20 dB above that of the narrow-band masker. They concluded that this decrease in threshold was a demonstration of suppression in simultaneous masking. Here it is argued that Fastl and Bechly’s results simply reflect the poorer detectability of signals masked by higher-frequency fluctuating maskers (their narrow-band masker) than by relatively flat-envelope maskers (their composite narrow-band plus tonal masker). The results of three experiments support the masker-envelope explanation. In the first experiment, as in the report of Fastl and Bechly, the masker centered at 1000 Hz (M1) was a narrow-band noise and the masker centered at 1150 Hz (M2) was a tone. Fastl and Bechly’s result was replicated. However, thresholds obtained when M1 was presented alone (the M1-only condition) were more affected by the starting level of the signal within each adaptive track than were thresholds obtained when M1 and M2 were presented together (the M1+M2 condition). This result paralleled a previous report that starting level influenced performance more with fluctuating than with flat-envelope maskers.

For the four of seven subjects who showed learning, there was also more improvement in the M1-only than in the M1+M2 condition. In the second experiment, M1 was a tone and M2 was a narrow-band noise. Thresholds were higher in the M1+M2 than in the M1-only condition, presumably due to the increased masker fluctuations in the M1+M2 condition. Finally, in the third experiment, there was little or no difference in threshold in the M1-only and M1+M2 conditions for the majority of subjects when M1 and M2 were both tones. Caution is advised in interpreting a release from masking as suppression. The failure to demonstrate suppression in simultaneous masking for the majority of subjects, using an off-frequency signal and stimuli relatively free of the confounding influence of envelope fluctuations, is in contrast to a prediction that suppression in simultaneous masking should be revealed if the masker and signal have different frequencies and thus are not equally influenced by the suppression effect.
Estimation of sediment volume scattering cross section and absorption loss coefficient
Authors: Stewart Robert A. , Chotiros Nicholas P.
Published: October 2005

A simple theoretical model for estimating the sediment volume scattering cross section and the absorption loss coefficient from the reverberation tail of an acoustic pulse observed by a point receiver within the ocean sediment is described. This model assumes an infinite plane wave entering the sediment at normal incidence and scattering isotropically from a uniform field of random point scatterers. The model predicts the magnitude and decay rate of the volume scattering at a point receiver in terms of the volume scattering cross section and the absorption coefficient of the medium. Experimental data were obtained from an array of in-sediment acoustic probes deployed at a site near Jacksonville, Florida, and Kings Bay, Georgia. By fitting the predictions of the model to experimentally observed volume scattering data, the volume scattering cross sections and absorption coefficients of real sediments were inferred. The absorption coefficient and volume scattering cross-section results were compared with attenuation measurements from core samples and with theoretical and experimental data from Hamilton [J. Acoust. Soc. Am. 68, 1313 (1980)], Nolle [J. Acoust. Soc. Am. 35, 1394–1408 (1963)], Turgut and Yamamoto [J. Acoust. Soc. Am. 87, 2376 (1990)], and Jackson et al. [J. Acoust. Soc. Am. 79, 1410 (1986)].
Temporal measures of anticipatory labial coarticulation for the vowel /u/: Within- and cross-subject variability
Authors: Perkell Joseph S. , Matthies Melanie L.
Published: October 2005

The timing of upper lip protrusion movements and accompanying acoustic events was examined for multiple repetitions of word pairs such as ‘‘lee coot’’ and ‘‘leaked coot’’ by four speakers of American English. The duration of the intervocalic consonant string was manipulated by using various combinations of /s/, /t/, /k/, /h/, and /♯/. Pairwise comparisons were made of consonant string duration (acoustic /i/ offset to acoustic /u/ onset) with durations of: protrusion movement beginning to acoustic /u/ onset, maximum acceleration of the movement to acoustic /u/ onset, and acoustic /u/ onset to movement end. There were some consonant-specific protrusion effects, primarily on the movement beginning event for /s/. Inferences from measures of the maximum acceleration and movement end events for the non-/s/ subset suggested the simultaneous and variable expression of three competing constraints: (1) end the protrusion movement during the voiced part of the /u/; (2) use a preferred movement duration; and (3) begin the /u/-related protrusion movement when permitted by relaxation of the perceptually motivated constraint that the preceding /i/ be unrounded. The subjects differed in the degree of expression of each constraint, but the results generally indicate that anticipatory coarticulation of lip protrusion is influenced both by acoustic-phonetic context dependencies and dynamical properties of movements. Because of the extensive variation in the data and the small number of subjects, these ideas are tentative; additional work is needed to explore them further.
An adaptive controller for the active absorption of sound
Authors: Orduña-Bustamante F. , Nelson P. A.
Published: October 2005

An adaptive system is presented that allows a secondary acoustic source to become an active absorber of sound at the end of a closed duct. The system can also be generalized in order to achieve other termination impedances. The system consists of a loudspeaker, two microphones, and signal processing hardware including a digital signal microprocessor. The signals from the microphones are processed to obtain an error signal that represents the difference between the actual and the desired acoustic impedance of the termination. An absorbing termination requires, for example, that the microphone pair acts as a unidirectional probe picking up the sound reflected from the active termination only. This signal is used as the error signal that the digital controller is required to minimize. A simple analysis shows that this can be done adaptively using the ‘‘filtered-X’’ LMS algorithm. A simple experimental setup is used to obtain an absorbing termination which is shown to work with periodic, random, and transient input signals.
Visual-auditory integration and vocalic effects on fricative perception.
Authors: Takagi Naoyuki , Mann Virginia
Published: October 2005

This study investigates the effect of visual presentation of four syllables ([sa], [sha], [su], [shu]) on perception of a fricative noise continuum. The visual stimuli were taken from videotapes of a speaker uttering the four syllables. The nine-step noise continuum ranged from [s] to [sh], and when followed by the acoustic vocalic portions taken from natural utterances of [sa], etc., replicated Mann and Repp’s (1980) findings about the context effects of vowel lip rounding and consonant place of articulation on fricative perception. To determine if similar context effects would occur when the vocalic information was specified visually rather than auditorily, stimuli from the noise continuum were dubbed in place of the natural utterances on the video tapes and subjects identified the visual-auditory hybrids by naming each syllable aloud. The results showed a significant lip rounding effect on perception of ‘‘s’’ vs ‘‘sh’’ indicating that listeners’ compensation for the decrease in frication noise frequency that is caused by anticipatory lip rounding takes place whether the lip rounding is perceived visually or auditorily. The effect of consonant place of articulation was less consistent.
Effects of lateral inhomogeneity on the geoacoustic properties of sediment.
Authors: Stoll Robert D. , Bryan George M.
Published: October 2005

Dispersion analysis of interface waves (Scholte/Stoneley/Rayleigh) has been used extensively to determine geoacoustic models of near-bottom ocean sediments. In many cases a single trace has been analyzed to derive group velocity dispersion using a multiple filter technique. The dispersion curve obtained in this manner reflects the average influence of the sediment acoustic properties over the entire path from source to receiver. However, when a linear array of receivers is used to obtain data simultaneously at a number of different ranges, it is possible to derive both group and phase velocity dispersion curves that correspond to propagation over a short portion (typically 5 m) of the total path at many different ranges. With this kind of data, the range-dependent variation of geoacoustic properties in the sediment may be assessed. Results are presented based on data obtained with a 24-receiver array and an explosive source, both deployed on the seafloor. Analysis of data from a number of different locations, mainly in shallow water ranging in depth from a few meters to 250 m, suggests that there is a considerable amount of lateral inhomogeneity even over very short ranges. [Work supported by ONR, Code 1125OA.]
Biologically inspired approaches for reduced order control of distributed elastic systems.
Authors: Carneal James P. , Fuller Chris R.
Published: October 2005

The control of distributed systems by multiple piezoelectric actuators has shown much promise. However for higher modal densities, many actuators are required and the order of the controller (i.e., number of channels) becomes large, leading to implementation problems and performance degradation. In this paper, a control approach, which was largely inspired by biological systems, is analytically investigated so as to reduce the order of the main controller. The inspiration for the system was derived from biological muscle control, where one main signal from the brain is sent to a large area of muscle tissue, but is processed locally by cell action into multiple subsequent signals for individual muscle cell elongation or contraction. In the present study, the system to be controlled consists of a simply supported beam excited by a harmonic point force disturbance. Control is attempted by multiple piezoelectric actuators attached to the beam surface. One actuator is chosen as the master actuator and is under direction of the main controller. The other (slave) actuators derive their control inputs by localized learning rules related to the behavior of their neighbor actuators. The master actuator uses linear quadratic optimal control theory while very simple local learning rules are employed to minimize beam vibrational energy density. The results presented demonstrate that the use of the multiple slave actuators in conjunction with the main channel of control significantly enhances control performance over the single actuator case, particularly for off resonance cases, by reducing control spillover. [Work supported by NASA Langley and ONR.]
Making and hearing the vocal trill: An acoustical study.
Authors: Castellengo Michèle , Colas Damien
Published: October 2005

Among vocal ornaments trill is the least well known. Several records of trills done by great singers have been analyzed in order to define and measure relevant characteristics for this ornament: the amplitude of the vibrato during the preparation, the extension and speed of the trill itself, the termination pattern. The importance of the accompanying amplitude modulation has also been investigated. An hypothesis for the particular vocal technique of bass singers is proposed. These various acoustical parameters are used as data for digital synthesis based on formant-waveform algorithm. Artificial vocal sequences are tested by subjects in order to evaluate the perceptual effect of the variations of the acoustical parameters and to appreciate the relative importance of the different elements of a trill. These experiments have pointed out the great importance of the preparation phase for perceiving a trill, and appreciating its interval (major or minor).
Effect of randomly inhomogeneous seafloor on the reflection and scattering of plane acoustic waves in shallow waters.
Authors: Badiey Mohsen , Cheng Alexander H.-D. , Jaya Indra , McGeary Susan , Schulkin Morris
Published: October 2005

The bottom of the ocean is composed of randomly inhomogeneous, anisotropic layers of sediments. A geoacoustic data set is constructed from previously measured geological experiments in shallow-water regions of the New Jersey Continental Shelf. This data set is used as input for a stochastic reflection model based on the Monte Carlo technique in order to study the effect of the random variations of the seafloor properties on the scattering and reflection of acoustic plane waves in a shallow ocean. It is found that the random inhomogeneities as well as the anisotropy of the subsurface are major causes of volume scattering and certain anomalies in the reflection coefficient.
Separation of trends and subharmonic structures from random variations in fundamental frequency and amplitude.
Authors: Berry David A. , Titze Ingo R.
Published: October 2005

An implicit assumption in voice perturbation analysis is that one is dealing with small random variations in fundamental frequency and amplitude. However, many irregularities in voiced speech are not necessarily small or random (e.g., subharmonics, amplitude modulations, frequency modulations, linear trends). In this study, various processing schemes are employed to detect/remove trends and subharmonics from fundamental frequency and amplitude contours. Voice perturbation measures are calculated before and after application of the detection/removal techniques. Separating trends and subharmonics from random perturbations in voice analysis may prove useful in classifying and identifying voice disorders. Results of analysis on a variety of subjects will be presented.
Frequency of quadrupole mode oscillations of spheroidal liquid drops in an acoustic field.
Authors: Zheng Xiaoyu , Tian Yuren , Holt R. Glynn , Apfel Robert E.
Published: October 2005

Ultrasonic levitation of liquid drops in air has been used [Y. Tian etal., J. Colloid Interface Sci. (submitted)] as a technique for measurement of the rheological properties (viscosity, interfacial tension, elasticity) of liquid surfaces and interfaces. The unavoidable deformation and asymmetry caused by the intensity of the sound field needed to levitate millimeter-sized water drops in air in a 1-g environment gives rise to a change in the frequency of quadrupole mode shape oscillations from the spherical value. This complicates measurements of rheological properties. Thus the frequency change due to the interaction with the sound field has been modeled. Using a unique conservation of energy approach, the shift due strictly to geometrical deformation of arbitrary origin is derived. Then realistic values of deformation and corresponding radiation force for typical cases are considered, modifying the previously obtained frequency shift values. Results are compared to experimental values obtained for millimeter-sized drops levitated ultrasonically in air in a 1-g field. [Work supported by NASA through JPL Contract No. 958722.]
VOT in Norwegian stops.
Authors: Halvorsen Berit
Published: October 2005

The stops from three Norwegian dialect areas [Eastern Norwegian (EN), Tro/nder dialects (TD), and the Bergen dialect] were recorded. Native speakers of Norwegian read mono- and disyllabic words twice in a carrier phrase. Stressed vowels were [e:], [eh], [u:], and [closed omega]. All three dialects have /bd open gee ptk/, EN and TD have retroflex stops /hooked tee hooked dee/ and TD also have palatal stops /c inverted eff/. Measurements of VOT were made using a wave-editing program at Haskins Laboratories. It was hypothesized that (1) the traditionally labeled ‘‘voiced’’ stops would have zero or short lag onset. This turned out to be the case for most of the speakers, but some of them had extraordinarily long lead onsets. Free speech from the same subjects showed no or smaller lead onsets in /bd open gee/, however. (2) VOT in labials <dentals/alveolars<velars. Measurements showed clear distinction in VOT between labial and dental/alveolar stops, but there was smaller difference in VOT for dentals/alveolars and velars. These results will be corroborated with perception tests with synthesized stops in CV syllables. [Work supported by the Norwegian Research Council for the Humanities.]
Experimental investigation on the amplification of hydrodynamic noise generation by the insertion of bubbles in a turbulent flow.
Authors: Hughes Charlene E. , Korman Murray S.
Published: October 2005

An apparatus is constructed to produce a turbulent shear flow that is generated by a submerged circular jet. The jet is arranged to flow in an upright position. Comparisons are made of the near-field hydrodynamic flow noise, when the jet flow becomes a composition of two-phase flow that consists of air bubbles in water. The near-field flow noise is measured by a hydrophone located at the point, four nozzle diameters from the exit and four nozzle diameters perpendicular to the jet axis. Preliminary results indicate that the acoustic spectra are greatly amplified in the case where the bubbles are introduced into the flow. Measurements of the acoustic intensity are made as a function of void fraction β (the ratio of air volume to total volume) in an effort to verify the theoretical amplification predictions made by Crighton and Ffowcs-Williams [J. Fluid Mech. 36, 585–603 (1969)] and more recently by Prosperetti [J. Acoust. Soc. Am. 84, 1042–1054 (1988)]. Tests are performed in the U.S. Naval Academy Hydrodynamics Tow Tank. [This research is a continuation of the work on ocean noise mechanisms that is supported by the National Center for Physical Acoustics and the ONR.]
Matched-field inversion of geoacoustic model parameters using unguided simulated annealing.
Authors: Lindsay Colin , Chapman N. R.
Published: October 2005

A method has been developed for the estimation of geoacoustic model parameters by inversion of acoustic field data using a nonlinear optimization procedure based on simulated annealing. The cost function used by the algorithm is the Bartlett matched-field processor which relates the measured acoustic field with replica fields calculated by the safari program. Model parameters are perturbed randomly over a specified range, and the algorithm searches the multidimensional parameter space of ocean bottom models to determine the parameter set corresponding to the best replica field. Convergence is driven by adaptively restricting the search space to regions with above-average values of the matched-field correlation. This approach removes the need for a predetermined annealing schedule. The performance of the method is demonstrated for a vertical line array in a shallow-water environment where the bottom consists of homogeneous elastic solid layers. Simulated data were used to study the effects of noise contamination, undersampling of the pressure field and uncertainty of the experimental geometry on parameter estimation. Results are presented for the inversion of data obtained in an experiment off the West Coast of Vancouver Island.
Propagation of finite amplitude sound in a waveguide with a parabolic sound velocity profile.
Authors: Reckamp Douglas E. , Zabolotskaya Evgenia A. , Hamilton Mark F.
Published: October 2005

The propagation of finite amplitude sound in a waveguide with a parabolic sound velocity profile is investigated theoretically. It is assumed that the primary wave propagates in a single mode at a frequency that is large compared with the cutoff frequency. The acoustic energy is therefore concentrated near the axis of the sound channel. Both the primary wave and the nonlinearly generated second harmonic component have mode shapes that are described by Gauss–Hermite eigenfunctions. For a primary wave in mode m, the second harmonic component is generated in all even-order modes up to 2m, with most of the energy contained in mode 2m. A nonlinear Schrödinger equation is derived for the envelope of a narrow-band pulse that propagates in a single mode. Analytical expressions are derived for the coefficients in the Schrödinger equation, and it is found that only dark envelope solitons can propagate without distortion in the waveguide. [DER was supported by the ARL Naval Academy Scholarship, EAZ and MFH by the David and Lucile Packard Foundation and by the Office of Naval Research.]
Veering winds, directionally opposing seas, and double-frequency pressure fluctuations at the sea floor.
Authors: Herbers T. H. C. , Guza R. T.
Published: October 2005

A 24-element array of pressure transducers (aperture 250×250 m) was deployed on the seafloor in 13-m depth, 2 km offshore of Duck, NC, to investigate the generation mechanisms of double-frequency (0.3–0.7 Hz) pressure fluctuations. Dramatic increases in pressure energy levels at about double the frequencies of locally generated seas consistently occur after sudden large shifts in local wind direction. The observed double-frequency energy levels agree well with predictions based on weakly nonlinear wave theory [K. Hasselmann, J. Fluid Mech. 12, 481–500 (1962)] and the observed frequency-directional spectra of swell and sea, confirming that the double-frequency pressure fluctuations are long-wavelength secondary waves forced by nonlinear interactions between nearly directionally opposing seas. Third-order statistics show the theoretically expected phase-coupling between opposing seas and double-frequency pressure fluctuations. Estimates of wave numbers and propagation directions demonstrate that the double-frequency pressure fluctuations have the theoretically predicted sum vector wave number of the interacting seas.
Kink-assisted mode hopping in a resonator.
Authors: Denardo Bruce , Larraza Andrés , McClelland Charles
Published: October 2005

For a sufficiently large fixed drive amplitude, a localized kink structure is observed to spontaneously participate in the transition of one standing wave mode to another as the drive frequency is slowly changed. The observations are of gravity waves in a parametrically driven annular channel of liquid. The kink, which can occur at any location around the resonator, has a substantially greater amplitude and shorter wavelength than the extended mode region. Such a structure is predicted to exist according to a theory that simultaneously allows amplitude and wave-number modulations of a finite-amplitude standing wave. The situation is in fundamental contrast to nonlinear Schrödinger (NLS) solitons, which correspond to only amplitude modulations, and to all other known types of solitons. Observations and theory of the NLS structures will be reviewed, and their role in the discovery of the new kinks will be discussed. The possibility of propagating versions of the new kinks, and of applications to fiber optic communications, will also be discussed.
New electrostrictive ceramics for sonar projector applications.
Authors: Rittenmyer Kurt M. , Ting R. Y.
Published: October 2005

Relaxor ferroelectric ceramics, in particular lead magnesium niobate–lead titanate (Pb3MgNb2O9–PbTiO3) compositions, have potential for hydroacoustic transducer applications. In an unbiased state, the strain-versus-electric field relationship is nonlinear (largely quadratic) with respect to the electric polarization. By applying a large dc bias voltage simultaneously with a small ac signal, acoustic signals whose amplitudes are linear with respect to the ac signal are produced. The strains produced are of similar magnitude to those of lead zirconate–titanate ceramics. Several specific compositions have been examined in order to optimize the material by reducing the dielectric and electromechanical hysteresis, the temperature dependence of dielectric properties, and the dielectric aging and the results are discussed. The possibility of being able to switch the polarization of the material off with the biasing field makes the further development of these materials intriguing. [This work supported by ONR.]
Application of the reverberation-limited form of the sonar equation to dolphin echolocation
Authors: Au Whitlow W. L.
Published: October 2005

The target detection range of two echolocating Atlantic Bottlenose dolphins as a function of target depth in Kaneohe Bay, Hawaii, was determined by Murchison [A. E. Murchison, Ph.D. dissertation, Univ. of Calif., Santa Cruz (1980)]. The threshold range decreased monotonically as the depth of the 6.35-cm-diam solid-steel sphere increased and approached the bottom. For the target lying on the bottom, the 50% correct detection threshold detection range was approximately 70 m. The scattering strength of the bottom in Kaneohe Bay at approximately the same location of the Murchison’s experiment was recently measured using a simulated dolphin echolocation signal and a transducer tilted at the appropriate grazing angle. The bottom scattering strength along with the target strength of the 6.35-cm sphere and the dolphin threshold range were incorporated into the generalized form of the sonar equation for a reverberation-limited situation and a detection threshold of 4.0 dB was calculated. This detection threshold compared well with the 2.3 dB obtained in an experiment in which the dolphin was required to detect a target in the presence of a clutter screen.
Acoustics and perception of overtone singing
Authors: Bloothooft Gerrit , Bringmann Eldrid , van Cappellen Marieke , van Luipen Jolanda B. , Thomassen Koen P.
Published: October 2005

Overtone singing, a technique of Asian origin, is a special type of voice production resulting in a very pronounced, high and separate tone that can be heard over a more or less constant drone. An acoustic analysis is presented of the phenomenon and the results are described in terms of the classical theory of speech production. The overtone sound may be interpreted as the result of an interaction of closely spaced formants. For the lower overtones, these may be the first and second formant, separated from the lower harmonics by a nasal pole-zero pair, as the result of a nasalized articulation shifting from /c/ to /a/, or, as an alternative, the second formant alone, separated from the first formant by the nasal pole-zero pair, again as the result of a nasalized articulation around /c/. For overtones with a frequency higher than 800 Hz, the overtone sound can be explained as a combination of the second and third formant as the result of a careful, retroflex, and rounded articulation from /c/, via schwa /E/ to /y/ and /i/ for the highest overtones. The results indicate a firm and relatively long closure of the glottis during overtone phonation. The corresponding short open duration of the glottis introduces a glottal formant that may enhance the amplitude of the intended overtone. Perception experiments showed that listeners categorized the overtone sounds differently from normally sung vowels, which possibly has its basis in an independent perception of the small bandwidth of the resonance underlying the overtone. Their verbal judgments were in agreement with the presented phonetic-acoustic explanation.
Modeling phoneme perception. I: Categorical perception
Authors: Schouten M. E. H. , van Hessen A. J.
Published: October 2005

On the basis of a number of vowel and stop-consonant discrimination experiments (AX and 2IFC fixed and roving) with natural stimuli, it is concluded that stop-consonant perception is highly categorical: there were few significant differences between the discrimination results and the phoneme identification results. Moreover, the discrimination and identification response maxima differed significantly from the other data points. Vowel perception was much less categorical: the maxima in the functions were much less significant, and there were significant differences between the various paradigms. Consonant discrimination was much less (if at all) subject to range effects than vowel discrimination. All these results point to different memory types for stop consonants and vowels, and, consequently, to a combination of two different theories of speech sound discrimination: dual-process theory (DPT) for consonants, and trace-context theory (TCT) for vowels.
A high-order adaptive integration method for wave propagation in range-independent fluid–solid media
Authors: Ivansson Sven , Karasalo Ilkka
Published: October 2005

Efficient computation of the Hankel-transform integral for the wave field in a laterally homogeneous fluid–solid medium is nontrivial, since the integrand may be both oscillating and irregularly peaked. We propose a high-order, adaptive integration method suitable for integrands with these characteristics. The method combines trapezoidal or Filon sums, obtained with several step sizes, with polynomial or Bulirsch–Stoer rational extrapolation to increase the order of convergence and to obtain error estimates. This technique is combined with adaptive interval halving, maintaining a hierarchy of subintervals, meshes, and function values in a stack to eliminate duplicate function evaluations. Computational results from an underwater acoustics application are presented. At any level of accuracy, the proposed method requires less computational work than nonadaptive trapezoidal or Filon quadrature, the difference growing to orders of magnitude as the accuracy increases.
Laboratory scale measurements and numerical predictions of underwater sound propagation over a sediment layer
Authors: Glegg Stewart A. L. , Hundley Allen J. , Riley Joseph M. , Yuan Jianren , Überall Herbert
Published: October 2005

A detailed set of measurements has been obtained using a model of a typical shallow-water channel, which included both a sediment and a substrate, and the results have been compared with numerical prediction codes. Good agreement with the numerical calculations of the acoustic field was obtained at high frequencies if the input parameters were optimized, within realistic bounds of their measured values.
Estimation of the spatial variability of transmission losses at low frequency in shallow water using multichannel seismic reflection data
Authors: Purdy G. M. , DuBois D. L. , Ewing J. I.
Published: October 2005

Spectral studies of commercial marine multichannel reflection profiling data demonstrate their utility for providing estimates of the degree of spatial variability in low-frequency (<100-Hz) transmission characteristics that is present in contrasting shallow water environments. The excellent spatial sampling provided by these readily available datasets allow them to resolve ∼10-dB changes in returned energy levels occurring over distances of as little as a few hundred meters. At frequencies below the cutoff frequency, when the wave field is no longer dominated by water-borne energy, these small scale variabilities in transmission losses cannot be straightforwardly predicted from routinely collected mapping data (e.g., reflection profiles and velocity analyses of pre-critical reflections). Existing commercial marine multichannel reflection profiling datasets constitute an important resource for the mapping of changes in propagation characteristics in shallow water.
Sound scattering by rough elongated elastic objects. I: Means of scattered field
Authors: Stanton T. K.
Published: October 2005

By use of the recently published deformed cylinder formulation [T. K. Stanton, J. Acoust. Soc. Am. 86, 691–705 (1989)], the scattered field due to rough elongated dense elastic objects is derived. The (one-dimensional) roughness is characterized by axial variations of radius. Explicit expressions are derived describing both the mean and mean square of the stochastic scattered field for the rough straight finite length cylinder (broadside incidence) for both ka≪1 and ka≫1 (k is the acoustic wave number and a is the radius) while only the mean is calculated for the prolate spheroid, uniformly bent finite cylinder, and infinitely long cylinder for ka≫1 (again, all broadside incidence). The modal-series-based solution is used in the ka≪1 case as the modal solution simplifies to the sum of two terms (monopole and dipole-like terms). For ka≫1, a more convenient approximate ‘‘ray’’ solution is used in place of the modal series solution. The results show that (1) when ka≪1 the roughness-induced variations of the mean and mean-square scattered fields due to the rough straight finite cylinder depend on the roughness, but are independent of frequency—an effect that has no counterpart in the area of scattering by rough planar interfaces. (2) When ka≫1 the mean specular (geometrically reflected) and Rayleigh surface elastic waves of the scattered field of each object are attenuated due to the roughness and their variations are dependent upon the frequency. In addition, the (roughness-induced) attenuation of the Rayleigh wave depends on the number of times the wave has circumnavigated the object. The mean-square values for the straight finite cylinder are attenuated in a similar manner with the additional dependence upon the correlation distance of the surface.
Ultrasonic wave interaction with a thin anisotropic layer between two anisotropic solids: Exact and asymptotic-boundary-condition methods
Authors: Rokhlin S. I. , Huang W.
Published: October 2005

Boundary conditions introduced to model a thin anisotropic layer between two generally anisotropic solids are given. The model can be used to describe an imperfect anisotropic interface. The present results for anisotropic boundary conditions are a generalization of previous work valid for either an isotropic viscoelastic layer [J. Acoust. Soc. Am. 89, 503–515 (1991)] or an orthotropic layer with a plane of symmetry coinciding with the incident plane [J. Acoust. Soc. Am. 91, 1875–1887 (1992)]. The boundary conditions are represented by a 6×6 transfer matrix which relates six-dimensional vectors formed from stresses and displacements on each side of the interface. The transfer matrix is obtained as an asymptotic representation of the three-dimensional solution for a thin orthotropic layer of arbitrary orientation between two solids. Such boundary conditions couple the in-plane and out-of-plane stresses and displacements on the interface even for isotropic bodies. Interface imperfections are modeled by an interfacial multiphase orthotropic layer with effective elastic properties. This determines the elements in the transfer matrix which includes both interface stiffness and inertial terms. The results are illustrated by numerical examples of ultrasonic wave reflection from an imperfect interface between anisotropic solids. The applicability of the boundary condition approach is analyzed by comparison with the exact solutions, which are obtained by taking into account multiple reflections inside the layer. It is shown that for small layer thickness-to-wavelength ratio, the asymptotic transfer matrix describes accurately the dynamical behavior of a thin interfacial layer between two generally anisotropic media. Interface waves are also considered and illustrated numerically.
Temporal cues for consonant recognition: Training, talker generalization, and use in evaluation of cochlear implants
Authors: Van Tasell Dianne J. , Greenfield Donna G. , Logemann Joelle J. , Nelson David A.
Published: October 2005

Limited consonant phonemic information can be conveyed by the temporal characteristics of speech. In the two experiments reported here, the effects of practice and of multiple talkers on identification of temporal consonant information were evaluated. Naturally produced /aCa/ disyllables were used to create ‘‘temporal-only’’ stimuli having instantaneous amplitudes identical to the natural speech stimuli, but flat spectra. Practice improved normal-hearing subjects’ identification of temporal-only stimuli from a single talker over that reported earlier for a different group of unpracticed subjects [J. Acoust. Soc. Am. 82, 1152–1161 (1987)]. When the number of talkers was increased to six, however, performance was poorer than that observed for one talker, demonstrating that subjects had been able to learn the individual stimulus items derived from the speech of the single talker. Even after practice, subjects varied greatly in their abilities to extract temporal information related to consonant voicing and manner. Identification of consonant place was uniformly poor in the multiple-talker situation, indicating that for these stimuli consonant place is cued via spectral information. Comparison of consonant identification by users of multi-channel cochear implants showed that the implant users’ identification of temporal consonant information was largely within the range predicted from the normal data. In the instances where the implant users were performing especially well, they were identifying consonant place information at levels well beyond those predicted by the normal-subject data. Comparison of implant-user performance with the temporal-only data reported here can help determine whether the speech information available to the implant user consists of entirely temporal cues, or is augmented by spectral cues.