bluuebunny/crossref_metadata_2025 huggingface dataset:
Shock wave emission and cavitation bubble generation by picosecond and nanosecond optical breakdown in water
Authors: Vogel A. , Busch S. , Parlitz U.
Published: October 2005

Shock wave emission and cavitation bubble expansion after optical breakdown in water with Nd:YAG laser pulses of 30-ps and 6-ns duration is investigated for energies between 50 μJ and 10 mJ which are often used for intraocular laser surgery. Time-resolved photography is applied to measure the position of the shock front and the bubble wall as a function of time. The photographs are used to determine the shock front and bubble wall velocity as well as the shock wave pressure as a function of time or position. Calculations of the bubble formation and shock wave emission are performed using the Gilmore model of cavitation bubble dynamics and the Kirkwood–Bethe hypothesis. The calculations are based on the laser pulse duration, the size of the plasma, and the maximally expanded cavitation bubble, i.e., on easily measurable parameters. They yield the dynamics of the bubble wall, the pressure evolution inside the bubble, and pressure profiles in the surrounding liquid at fixed times after the start of the laser pulse. The results of the calculations agree well with the experimental data. A large percentage of the laser pulse energy (up to 72%) is transformed into the mechanical energy ES and EB of the shock wave and cavitation bubble, whereby the partitioning between ES and EB is approximately equal. 65%–85% of ES is dissipated during the first 10 mm of shock wave propagation. The pressure at the plasma rim ranges from 1300 MPa (50 μJ, 30 ps) to 7150 MPa (10 mJ, 6 ns). The calculated initial shock wave duration has values between 20 and 58 ns, the duration measured 10 mm away from the plasma is between 43 and 148 ns. A formation phase of the shock front occurs after the ns pulses, but not after the ps pulses where the shock front exists already 100 ps after the start of the laser pulse. After shock front formation, the pressure decays approximately proportional to r−2, and at pressure values below 100 MPa proportional to r−1.06. The maximum bubble wall velocity ranges from 390 to 2450 m/s. The calculations of bubble and shock wave dynamics can cover a large parameter range and may thus serve as a tool for the optimization of laser parameters in medical laser applications.
Numerical solution and a posteriori error estimation of exterior acoustics problems by a boundary element method at high wave numbers
Authors: Geng P. , Oden J. T. , Demkowicz L.
Published: October 2005

This paper is concerned with the application of boundary element methods to the exterior acoustical problem at high wave numbers. The major issues here are to establish a strong theoretical foundation for the application of the Burton–Miller integral equation and develop a practical way for its numerical implementation. Unlike many conventional approaches, the problem in this study is formulated by the Galerkin method. Through an analysis on its ellipticity, the Burton–Miller equation is proven to be well-posed in the H1/2-Sobolev space and its approximation can attain a quasioptimal convergence rate. The Galerkin method avoids sensitive properties of hypersingular integration, simplifies the numerical implementation, and improves the quality of the numerical solutions, especially at high wave numbers. An L2-norm residual error estimation technique is also implemented for an adaptive scheme for these problems. The numerical implementation is completed on parallel distributed-memory machines as well as conventional sequential machines. The validation of the method at high wave numbers is done through tests on a series of numerical examples.
Speechreading enhancement: A comparison of spatial-tactile display of voice fundamental frequency (F0) with auditory F0
Authors: Kishon-Rabin Liat , Boothroyd Arthur , Hanin Laurie
Published: October 2005

In two experiments, subjects repeated video-recorded sentences presented via speechreading with and without enhancement by a sensory input derived from the acoustic speech signal. Enhancement was measured as percentage increase in recognized words. In experiment 1, tactile presentation of fundamental frequency (F0) provided, after training, for three of four postlingually deafened adults a mean enhancement of 11%. In experiment 2, using six hearing adults, the auditory presentation of F0 provided a mean enhancement of 50%. This value fell, but only to 37%, when the F0 signal was derived from the processor of the tactile aid used in experiment 1. From these experiments it can be concluded that the unexpectedly small enhancement found in experiment 1 is probably due both to the fact that this tactile aid was not providing effective access to all of the information available in the F0 contour and to limitations related to the tactile processing ability of the kinaesthetic system.
Nonlinear dynamical analysis of speech
Authors: Kumar Arun , Mullick S. K.
Published: October 2005

This paper reports results of the estimation of dynamical invariants, namely Lyapunov exponents, dimension, and metric entropy for speech signals. Two optimality criteria from dynamical systems literature, namely singular value decomposition method and the redundancy method, are used to reconstruct state space trajectories of speech and make observations. The positive values of the largest Lyapunov exponent of speech signals in the form of phoneme articulations show the average exponential divergence of nearby trajectories in the reconstructed state space. The dimension of a time series is a measure of its complexity and gives bounds on the number of state space variables needed to model it. It is found that most speech signals in the form of phoneme articulations are low dimensional. For comparison, a statistical model of a speech time series is also used to estimate the correlation dimension. The second-order dynamical entropy (which is a lower bound of metric entropy) of speech time series is found to be positive. This independently corroborates the interpretation of the largest Lyapunov exponent results and gives an estimate of the predictability time.
Common tone adaptive tuning using genetic algorithms
Authors: Horner Andrew , Ayers Lydia
Published: October 2005

This paper introduces a genetic algorithm method for adaptive tuning of chord sequences. The algorithm retains the tunings of common tones from previous chords, and adjusts the tunings of the other notes. The genetic algorithm method avoids problems associated with simpler enumerative, greedy, and distributive tuning strategies. The paper gives results for several musical examples using several different error measures, with extended results for minimizing the worst tuning error among harmonic thirds and fifths.
The dynamics of expressive piano performance: Schumann’s ‘‘Träumerei’’ revisited
Authors: Repp Bruno H.
Published: October 2005

Ten graduate student pianists were recorded playing Robert Schumann’s ‘‘Träumerei’’ three times on a Yamaha Disclavier. Their expressive dynamics were analyzed at the level of hammer (MIDI) velocities. Individual dynamic profiles were similar across repeated performances, more so for the right hand (soprano and alto voices) than for the left hand (tenor and bass voices). As expected, the soprano voice, which usually had the principal melody, was played with greater force than the other voices, which gained prominence only when they carried temporarily important melodic fragments. Independent of this voice differentiation, there was a tendency for velocity to increase with pitch, at least in the soprano and alto voices. While there was an overall tendency for velocities to increase with local tempo, there were salient local departures from this coupling. Individual differences in expressive dynamics were not striking and were only weakly related to individual differences in expressive timing.
Flow noise calculations for extended hydrophones in fluid- and solid-filled towed arrays
Authors: Knight Andrew
Published: October 2005

Towed arrays of hydrophones are used as large aperture sonars by the seismic industry and by many navies. Flow noise originating in the turbulent boundary layer often limits the performance of these sonars. The flow noise can be reduced by filtering certain wave numbers using an elastic tube, groups of hydrophones, or extended hydrophones. The amount of noise reduction is investigated in cylindrical geometry for different extended hydrophones, and for solid- and fluid-filled tubes.
Emission of sound by a semi-submerged object in shallow water
Authors: Og̃uz H. N.
Published: October 2005

A semi-analytical solution to the problem of noise emission by a finite size object in shallow water is described. The acoustic field near the object is formulated in spherical coordinates. An inner region is set up to satisfy bottom boundary conditions and the normal mode solution of the outer region is matched at some distance from the source. Several numerical examples related to noise emission from bubble clouds are given. Comparison with the method of images shows excellent agreement up to a certain distance from the source where the image solution is expected to be accurate. The technique is also extended to handle arbitrary sound-speed profiles in water column by means of a novel method for calculating normal modes. The point source approximation that has been widely used in the literature is also discussed by comparing the normal mode coefficients. It is found that the validity of the point source solution depends very much on the local radiation characteristics of the source.
Statistical analysis of the power injection method
Authors: De Langhe K. , Sas P.
Published: October 2005

The power injection method (PIM) has become widely accepted as a valuable technique to predict the statistical energy analysis (SEA) parameters of a structure in situ. PIM requires the measurement of the power input into every single subsystem and the measurement of the energy level of every subsystem. By inverting the appropriate measured energy matrix, the SEA parameters can be obtained. Conventional PIM suggests to use a more or less predefined number of excitation and response locations. Most often three excitation and five response locations are taken. Due to the spatial variation of the energy density in a subsystem, there will always be a substantial variability associated with the space-averaged energy of vibration and hence associated with the SEA parameters. An accurate SEA model requires accurately measured space averaged energies of vibration and power input levels. The accuracy of the SEA parameters can be assessed by evaluating the confidence levels of the so-called ‘‘normalized energy levels’’ and by converting these values into confidence levels of the SEA parameters. This paper aims at presenting the identification procedure of the statistics of the SEA parameters as a function of the number of excitation and response points taken into account during the PIM measurements. In the first place, emphasis will be given to the presentation of the equations dealing with the essential statistical properties of the SEA parameters. It will be shown that by applying straightforward formulas it is possible to assess the accuracy of the estimated SEA parameters and to assess the accuracy of the SEA applications, i.e., vibration prediction, source localization, power flow analysis, sensitivity analysis, etc. Some formulas which are given in this respect will be illustrated by means of SEA results on an irregular box-type structure.
A theoretical and simulation study of acoustic normal mode coupling effects due to the Barents Sea Polar Front, with applications to acoustic tomography and matched-field processing
Authors: Jin Guoliang , Lynch James F. , Chiu Ching Sang , Miller James H.
Published: October 2005

Normal mode coupling due to a shallow water coastal front is considered, using oceanographic data from the 1992 Barents Sea Polar Front (BSPF) experiment as input to normal mode and parabolic equation (PE) acoustic propagation models. Criteria for the sensitivity of mode coupling to coastal front widths are derived, and applied to the BSPF as a representative example. The effects of coastal fronts on tomographic schemes are considered, particularly in terms of travel time-based tomography. The effects of frontal mode coupling on matched-field processing schemes are also considered, using both the maximum likelihood and variable coefficient likelihood methods, which show differing sensitivities to mismatch. Finally, directions for future research are discussed.
A mixed experimental and theoretical method for noise propagation and radiation prediction of a cowled axial fan
Authors: Lazreq Z. , Tahar M. Ben , Ville J. M. , Auger J. M.
Published: October 2005

A method for predicting acoustic pressure radiated by a duct opening with internal axial flow, based upon mixed experimental and numerical tools, is presented. It is applied to a six-bladed/one stator configuration axial fan cowled by a cylindrical duct 2.3 m long, 0.6 m in diameter and carrying a low-speed axial flow (M0≤0.1). Experimental mappings of acoustic pressure, acoustic axial particle velocity, and axial mean flow velocity at blade passing frequencies upstream of the rotor are carried out using a probe made of a microphone and a single hot wire. The results show an acoustic field structure as expected by acoustic propagation laws in ducts. After a modal filtering, experimental radial acoustic potential profiles are input to the database for the prediction process. In the second step, the theoretical radiated far field is computed using a program based on a variational formulation by integral equations accounting for internal flow. The very good agreement between theoretical and experimental results demonstrates the validity of this method.
Comparison of algorithms for solving parabolic wave equations
Authors: Collins Michael D. , Cederberg R. J. , King David B. , Chin-Bing Stanley A.
Published: October 2005

The three types of algorithms that have been developed for solving parabolic wave equations are compared. Until recently, it was necessary to choose between the finite-difference and split-step Fourier algorithms and make a trade-off between efficiency and capability. Test problems are presented to illustrate the efficiency of the split-step Padé algorithm, which provides the capability of the finite-difference algorithm. For deep water problems, the split-step Padé algorithm provides efficiency comparable to the split-step Fourier algorithm. For the shallow water problems that are currently of interest, the split-step Padé algorithm can be more than an order of magnitude faster than the split-step Fourier algorithm.
Staggered-grid pseudospectral viscoacoustic wave field simulation in two-dimensional media
Authors: Chen How-Wei
Published: October 2005

A viscoacoustic numerical modeling algorithm is developed, tested, and implemented for two-dimensional media. The loss mechanism is simulated according to a standard linear solid model. With anelastic effects defined through superposition of relaxation mechanisms, and incorporating them into the wave equation in terms of memory variables, the time-domain computation of responses of viscoacoustic media with arbitrary spatial variations is feasible. A numerical solution of viscoacoustic responses is obtained by solving either two-dimensional homogeneous or heterogeneous viscoacoustic wave equations. The model is parametrized through stress, strain relaxation times, density, relaxed and unrelaxed modulus, and velocity. On constructing P and S velocity, Qp, and Qs models separately, attenuated and decoupled propagating P and S wave fields are synthesized. According to this scheme one can model widely varying Q in highly heterogeneous media. Simulation of a pure acoustic wave field is regarded as a special case when temporally invariant stress and strain variables are considered. Through systematic analysis, a scheme with a staggered grid is highly desirable for stable computation and reduction of numerical artifacts such as grid dispersion and grid anisotropy. Considerable Nyquist error may arise when a regular grid for a first-derivative operator is used; a staggered grid enables significant improvement. Implementation of a pseudospectral technique with staggered grid provides a more general and more accurate description of wave propagation phenomena. Results from viscoacoustic simulation show that considerable variation of dynamic properties such as a decreased amplitude due to intrinsic Q and temporal shift due to physical wave dispersion phenomena can be analyzed quantitatively. Combined effects of source directivity, complex velocity and attenuation structures may alter significantly in the computed synthetic seismograms.
A plane-wave decomposition method for modeling scattering from objects and bathymetry in a waveguide
Authors: Fawcett John A.
Published: October 2005

In this paper a straightforward plane-wave decomposition method which can be used for solving object and/or interface scattering problems in a waveguide is described. The method utilizes the free-space scattering matrix of an object in conjunction with the medium’s interface and layer matrices in order to solve the waveguide scattering problem.
Bathymetric and volumetric contributions to ocean acoustic mode coupling
Authors: McDonald B. Edward
Published: October 2005

Ocean acoustic mode coupling matrix elements are investigated assuming weak range dependence in both the sound-speed profile and bathymetry. The range-dependent environmental variables are taken as known, and explicit integral expressions for the matrix elements are derived. The expressions contain separate volumetric and bathymetric terms arising from range dependence in the water column and bathymetry, respectively. The bathymetric terms lead to an algebraic connection between rates of modal ray curvature (horizontal refraction) due to bathymetry and energy loss rate due to bottom absorption. Theoretical evidence that a signal refracted by shallow bathymetry may show decreasing bottom absorption with increasing mode number is presented.
Modeling of seafloor wave propagation and acoustic scattering in 3-D heterogeneous media
Authors: Bradley Christopher R. , Stephen Ralph A.
Published: October 2005

Results from a 3-D finite difference code for the elastic wave equation are used to compare scattering from volume and surface heterogeneities at the seafloor. The 2-D and 3-D models for flat ocean crust containing volume heterogeneities, single facets, and statistically rough seafloors are compared. For both hard bottom (shear velocity greater than water velocity) and soft bottom (shear velocity less than water velocity) environments, heterogeneities scatter energy both forward and backward into the water column via three mechanisms: primary scattering from the direct compressional wave reflecting off the seafloor heterogeneities, secondary scattering from transmitted compressional and shear waves interacting with volume heterogeneities and from interface waves scattering from near surface heterogeneities, and tertiary scattering from interface waves spawning additional interface waves. There is significant secondary and tertiary scattering from rough, hard bottoms representative of basaltic seafloors. The results indicate that two-dimensional modeling techniques may be appropriate for modeling sub-bottom volume heterogeneities with velocity contrast less than 10% but may underestimate scattering from rough seafloors. It is also found that subsurface conversion to horizontally polarized shear waves is significant for both volume and surface heterogeneous crust in the three-dimensional model.
High-frequency surface acoustic wave devices at very low temperature: Application to loss mechanisms evaluation
Authors: El Habti A. , Bastien F. , Bigler E. , Thorvaldsson T.
Published: October 2005

Previous work on high-performance bulk wave resonators in the frequency range of 5 to 25 MHz has shown that, by cooling to liquid helium temperature, acoustic losses become negligible. Therefore other sources of losses can be precisely measured. A similar approach is followed in the present work for high-frequency surface wave resonators. Experiments have been performed at 416 MHz on quartz devices. It is shown that for surface waves propagating in a good surface acoustic wave (SAW) resonator an important source of acoustic loss is due to intrinsic acoustic losses. By cooling the device to below 30 K, the quality factor Q shows a T−4 dependence characteristic of intrinsic acoustic losses. Below 4–10 K a plateau region is reached. High Q values in the range of 1.5×105 have been obtained at 4.2 K for 416-MHz devices, yielding a Q×f product of 7.5×1013 almost as good as for cooled bulk devices. Another set of measurements on a lithium niobate (LiNbO3) resonator at 847 MHz does not give a significant increase of quality factor Q at low temperature. This is due to the presence of other loss mechanisms not related to intrinsic acoustic losses because the LiNbO3 resonator operates in a leaky mode rather than a Rayleigh mode. The applications of the method to the characterization of new kinds of SAW resonators will be helpful for optimizing high-Q surface wave resonators at high frequencies, based on new modes or new materials.
Laser ultrasonic signal processing: A model-reference approach
Authors: Candy J. V. , Thomas G. H. , Chinn D. J. , Spicer J. B.
Published: October 2005

A model-reference approach is developed to solve the signal enhancement problem of a laser ultrasonics application for nondestructive evaluation. In this problem a sophisticated laser thermoelastic propagation model is used to synthesize the surface displacement of the specimen under test. Once synthesized, this model response is used as the reference signal in an optimal (minimum error variance) signal enhancement scheme. Both fixed and adaptive processors are considered in this application where it is shown that a significant improvement in signal levels can be achieved over the usual methods to enhance noisy data acquired from a Michelson interferometric measurement system and increase its overall sensitivity.
Trapped torsional modes in solid cylinders
Authors: Johnson Ward , Auld B. A. , Segal E. , Passarelli F.
Published: October 2005

An approximate theory is presented for torsional modes in a solid cylinder having a larger-diameter central section. Modes in a narrow frequency range just above the cutoff of each branch are ‘‘trapped’’ such that, in long samples, the amplitudes decay exponentially with distance from the central section. To confirm the theory, measurements were performed on aluminum alloy cylinders using noncontacting electromagnetic-acoustic transduction. Vibrational amplitudes of a trapped mode measured as a function of position along the length of a sample are in good agreement with theoretical calculations. The resonant frequencies of three samples with different dimensions also closely match the theory for trapped modes. Additional generally weak resonances that are observed may be associated with torsional modes that vary sinusoidally along the entire length of the samples.
Robust source localization in an acoustic waveguide
Authors: Harrison Brian F. , Vaccaro Richard J. , Tufts Donald W.
Published: October 2005

Matched-field source localization methods attempt to estimate the range and depth of a source in an acoustic waveguide. These methods give good results when the waveguide parameters are known precisely; however, matched-field methods have been shown to be very sensitive to model mismatch resulting from errors in the assumed environmental parameters. Described in this paper is an approach which minimizes model mismatch, caused by uncertainty in the sound velocity profile, by jointly estimating the environmental parameters and source location. An efficient way to initialize the maximum-likelihood search by projecting the received data onto subspaces corresponding to regions in parameter space is proposed. Monte Carlo simulation results in a shallow-water environment are reported.
Two-tone rate suppression boundaries of cochlear ganglion neurons in normal chickens
Authors: Chen Lin , Salvi Richard J. , Trautwein Patricia G. , Powers Nicholas
Published: October 2005

The purpose of the present study was to provide a quantitative description of two-tone rate suppression boundaries in normal chickens. The boundaries were measured in 249 cochlear ganglion neurons using a tone 20 dB above threshold at the characteristic frequency (CF). The boundaries were present in 90.4% of neurons either on both sides or only one side of CF but more frequently above CF than below CF. The best suppression thresholds were positively correlated with and, on the average, 19–25 dB higher than CF thresholds. The boundary was farther from CF and shallower below CF than above CF. The boundary slope varied slightly with CF threshold and the tuning curve slope. These results are generally consistent with previous reports from mammals except that: (1) the boundary below CF did not follow and lie above the tuning curve flank; (2) the average best suppression threshold was slightly lower below CF than above CF; (3) the boundaries below and above CF were not particularly asymmetrical.
Vocal tract area functions from magnetic resonance imaging
Authors: Story Brad H. , Titze Ingo R. , Hoffman Eric A.
Published: October 2005

There have been considerable research efforts in the area of vocal tract modeling but there is still a small body of information regarding direct 3-D measurements of the vocal tract shape. The purpose of this study was to acquire, using magnetic resonance imaging (MRI), an inventory of speaker-specific, three-dimensional, vocal tract air space shapes that correspond to a particular set of vowels and consonants. A set of 18 shapes was obtained for one male subject who vocalized while being scanned for 12 vowels, 3 nasals, and 3 plosives. The 3-D shapes were analyzed to find the cross-sectional areas evaluated within planes always chosen to be perpendicular to the centerline extending from the glottis to the mouth to produce an ‘‘area function.’’ This paper provides a speaker-specific catalogue of area functions for 18 vocal tract shapes. Comparisons of formant locations extracted from the natural (recorded) speech of the imaged subject and from simulations using the newly acquired area functions show reasonable similarity but suggest that the imaged vocal tract shapes may be somewhat centralized. Additionally, comparisons of the area functions reported in this study are compared with those from four previous studies and demonstrate general similarities in shape but also obvious differences that can be attributed to differences in imaging techniques, image processing methods, and anatomical differences of the imaged subjects.
Cepstral representation of speech motivated by time–frequency masking: An application to speech recognition
Authors: Aikawa Kiyoaki , Singer Harald , Kawahara Hideki , Tohkura Yoh’ichi
Published: October 2005

A new spectral representation incorporating time–frequency forward masking is proposed. This masked spectral representation is efficiently represented by a quefrency domain parameter called dynamic-cepstrum (DyC). Automatic speech recognition experiments have demonstrated that DyC powerfully improves performance in phoneme classification and phrase recognition. This new spectral representation simulates a perceived spectrum. It enhances formant transition, which provides relevant cues for phoneme perception, while suppressing temporally stationary spectral properties, such as the effect of microphone frequency characteristics or the speaker-dependent time-invariant spectral feature. These features are advantageous for speaker-independent speech recognition. DyC can efficiently represent both the instantaneous and transitional aspects of a running spectrum with a vector of the same size as a conventional cepstrum. DyC is calculated from a cepstrum time sequence using a matrix lifter. Each column vector of the matrix lifter performs spectral smoothing. Smoothing characteristics are a function of the time interval between a masker and a signal. DyC outperformed a conventional cepstrum parameter obtained through linear predictive coding (LPC) analysis for both phoneme classification and phrase recognition by using hidden Markov models (HMMs). Compared with speaker-dependent recognition, an even greater improvement over the cepstrum parameter was found in speaker-independent speech recognition. Furthermore, DyC with only 16 coefficients exhibited higher speech recognition performance than a combination of the cepstrum and a delta-cepstrum with 32 coefficients for the classification experiment of phonemes contaminated by noises.
On the influence of loading on the velocity of guided acoustic waves propagating in linear elastic wedges
Authors: de Billy M.
Published: October 2005

It was demonstrated by V. V. Krylov [Ultrason. Symp. Cat. 94, CHO 793–796 (1994)] and J. R. Chamuel [IEEE Ultrason. Symp. 93, CHO 313–318 (1993)] that for wedges with small values of the apex angle, the water loading effect is a decrease of the velocity of propagation of the antisymmetic modes. The objective of this study is to quantify the loading effect on the velocity of propagation of the fundamental antisymmetric flexural (ASF) mode for large values of the apex angle (20°<φ<90°). The experimental results are limited to the lowest mode and are concerned with brass and Plexiglas linear wedges. It is demonstrated that the decrease of the velocity is more important as the mass densities ratio (ρliquid/ρsolid) increases.
Extrapolation of an empirical absorber formula to low frequencies
Authors: Behrens E. W.
Published: October 2005

A method to extrapolate an empirical absorber formula to low frequencies is presented which is based on a generalized Rayleigh model. The approach differs from Mechel’s method [Acustica 35, 210–213 (1976)] of extrapolation by not modifying the coefficients in the absorber formula but by suggesting a more general expression that matches the empirical formula at some appropriately chosen point and provides a differentiable continuation to zero frequency. The procedure is demonstrated on Delany’s and Bazley’s well-documented power law for fibrous absorbers, but it could be applied to any empirical formula that does not give reasonable results for low frequencies.
Template-based automatic recognition of birdsong syllables from continuous recordings
Authors: Anderson Sven E. , Dave Amish S. , Margoliash Daniel
Published: October 2005

The application of dynamic time warping (DTW) to the automated analysis of continuous recordings of animal vocalizations is evaluated. The DTW algorithm compares an input signal with a set of predefined templates representative of categories chosen by the investigator. It directly compares signal spectrograms, and identifies constituents and constituent boundaries, thus permitting the identification of a broad range of signals and signal components. When applied to vocalizations of an indigo bunting (Passerina cyanea) and a zebra finch (Taeniopygia guttata) collected from a low-clutter, low-noise environment, the recognizer identifies syllables in stereotyped songs and calls with greater than 97% accuracy. Syllables of the more variable and lower amplitude indigo bunting plastic song are identified with approximately 84% accuracy. Under restricted recording conditions, this technique apparently has general applicability to analysis of a variety of animal vocalizations and can dramatically decrease the amount of time spent on manual identification of vocalizations.
Modal impedances for nonaxisymmetric vibrations of a thin spherical shell
Authors: Evans Richard B.
Published: October 2005

Modal impedances are found by solving the equations of motion of a thin spherical shell in terms of nonaxisymmetric modes of vibration. These mechanical impedances relate the modal expansion coefficients of the applied force per unit area and the velocity of the shell. The application and interpretation of these modal impedances require an awareness of the lack of orthogonality of certain modes. In proper combinations, the modal impedances in the nonaxisymmetric case are found to be identical to known modal impedances in the axisymmetric case. The analysis is restricted to extensional effects of a thin shell with radial forcing.
Comments on ‘‘Effects of bandwidth on glottal airflow waveforms estimated by inverse filtering’’ [J. Acoust. Soc. Am. 98, 763–767 (1995)]
Authors: Strik Helmer
Published: October 2005

In the subject paper [Alku and Vilkman, J. Acoust. Soc. Am. 98, 763–767 (1995); hence AV], AV describe the results of their research on the effect of bandwidth on estimated voice source parameters. They found that reducing the bandwidth (by low-pass filtering the glottal flow signals) leads to a distortion of the estimated parameters. Although I do agree that low-pass filtering influences the estimate of the voice source parameters, I do not agree with some of their conclusions, explanations, and recommendations. Furthermore, the method they used does not seem to be optimal for the purpose of their research. These matters are discussed in this Letter.
An experimentally obtainable heat source due to absorption of ultrasound in biological media
Authors: Drewniak J. L. , Dunn F.
Published: October 2005

Deposition of heat as a result of loss in an ultrasonic wave may result in damage to biological tissues. The extensive use of ultrasound for diagnostic purposes during pregnancy necessitates the evaluation of thermal risk to a developing fetus during routine clinical exposures. Because of the small ultrasonic absorption coefficient in soft tissues at low megahertz frequencies, temperature elevations exceeding 1 °C are not expected from clinically employed ultrasound systems, and there is no evidence that such small temperature increases can result in deleterious effects. However, when the propagation path includes bone, which is known to be highly lossy, theoretical calculations and experimental work indicate that local heating might exceed 1 °C for realistic clinical conditions. Thus it is imperative to obtain reasonable estimates of the temperature elevation in and around fetal bone in order to assess risk. Because of a lack of measured data for the thermal and acoustic properties of fetal bone, which depend on gestational age, estimates of the temperature elevation resulting from exposure to ultrasound must be based on crude models. A measured quantity for a heat source resulting from conversion of acoustic to thermal energy in an ultrasound field is suggested. The heat source is developed from theoretical considerations, and can be used in the bioheat transfer equation to obtain better estimates of the temperature increase in fetal bone and the surrounding tissues as a result of exposure to ultrasound.
Acoustoelasticity theory and applications for fluid-saturated porous media
Authors: Grinfeld Michael A. , Norris Andrew N.
Published: October 2005

The general theory for small dynamic motion superimposed upon large static deformation, or acoustoelasticity, is developed for isotropic fluid-filled poroelastic solids. Formulas are obtained for the change in acoustic wave speeds for arbitrary loading, both on the frame and the pore fluid. Specific experiments are proposed to find the complete set of third-order elastic moduli for an isotropic poroelastic medium. Because of the larger number of third-order moduli involved, seven as compared with three for a simple elastic medium, experiments combining open-pore, closed-pore, jacketed, and unjacketed configurations are required. The details for each type of loading are presented, and a set of possible experiments is discussed. The present theory is applicable to fluid-saturated, biconnected porous solids, such as sandstones or consolidated granular media.
Frequency spectra of nonlinear elastic pulse-mode waves
Authors: Kadish Abraham , TenCate James A. , Johnson Paul A.
Published: October 2005

The frequency spectrum of simple waves is used to derive a closed form analytical representation for the frequency spectrum of damped nonlinear pulses in elastic materials. The damping modification of simple wave theory provides an efficient numerical method for calculating propagating wave forms. The spectral representation, which is neither pulse length nor amplitude limited, is used to obtain estimates for parameters of the nonlinear state relation for a sandstone sample from published experimental data, and the results are compared with those of other theories. The method should have broad application to many solids.
Measurements of third-order elastic constants in rocks
Authors: Winkler Kenneth W. , Liu Xingzhou
Published: October 2005

Measurements are reported of third-order elastic constants for nine rocks (sandstones, limestones, granite) and a few synthetic materials at ambient room conditions. Along with velocity, porosity, density, and uniaxial strength, these data constitute a unique database of rock properties. Third-order elasticity successfully describes a variety of acoustic phenomenon in many materials, and measurements exist of third-order elastic constants in metals, plastics, and crystals. A key feature of third-order elasticity theory is that acoustic velocities vary with the stress in a material. In spite of the fact that velocities in rocks are extremely stress dependent, no measurements have previously been published of third-order elastic constants in sedimentary rocks.
Gaussian ray bundles for modeling high-frequency propagation loss under shallow-water conditions
Authors: Weinberg Henry , Keenan Ruth Eta
Published: October 2005

An acoustical propagation model was developed to analyze high-frequency propagation loss under shallow-water conditions. The model is based on Gaussian ray bundles which are similar in form but somewhat simpler than Gaussian beams. After describing the approach, propagation loss predictions are compared with those of various ‘‘standard models’’ at lower frequencies where the latter models are accurate and efficient. If Gaussian ray bundles compare well at the lower frequencies, they should perform well at the higher frequencies as ray approximations improve.
The Riccati method for the Helmholtz equation
Authors: Lu Ya Yan , McLaughlin Joyce R.
Published: October 2005

The operator Riccati equation for the Dirichlet-to-Neumann map is derived from the exact operator factorization of the two-dimensional variable coefficient Helmholtz equation. Numerical schemes are developed for the operator Riccati equation and its variant using a local eigenfunction expansion. This leads to a practical computational method for acoustic wave propagation over large range distances, since the boundary value problem of the Helmholtz equation is reduced to ‘‘initial’’ value problems that are solved by marching in the range. The efficiency and accuracy of the method is demonstrated by numerical experiments including the plane-parallel range-dependent waveguide benchmark problem proposed by the Acoustical Society of America.
Combined volume and surface scattering in a channel using a modal formulation
Authors: Beran Mark J. , Frankenthal Shimshon
Published: October 2005

In previous work, a modal approach was used to study random volume scattering in a shallow channel [M. J. Beran and S. Frankenthal, J. Acoust. Soc. Am. 91, 3203–3211 (1992)]. Here, it is shown how to include the effects of a rough channel surface in the formulation. To include the effects of a rough surface, the modes are taken to be dependent on the range and transverse coordinates in addition to the depth coordinate. The propagation is studied in terms of the ensemble-averaged two-point coherence function and the equation governing the coherence function is derived. The general method is given in the above-cited article on volume scattering. In the present paper, it is shown how the surface scattering terms may be treated using the modal approach. In order to insure energy conservation when the generalized modal field equations are simplified, the parabolic approximation is replaced by a method which includes both forward and backward propagating fields. The two-point coherence function is expressed as the sum over both self-modal and cross-modal coherence functions. The differences between the equations governing the self-modal coherence functions and the cross-modal coherence functions are considered. A numerical example is presented which uses typical shallow water parameters. Figures are presented to show how the mode energies are transferred between the modes as the acoustical field propagates. The difference between the modal transfer of energy for volume scattering and for surface scattering is discussed.
Acoustic estimation of seafloor parameters: A radial basis functions approach
Authors: Caiti Andrea , Jesus Sergio M.
Published: October 2005

A novel approach to the estimation of seafloor geoacoustic parameters from the measurement of the acoustic field in the water column is introduced. The approach is based on the idea of approximating the inverse function that links the geoacoustic parameters with the measured field through a series expansion of radial basis functions. In particular, Gaussian basis functions are used in order to ensure continuity and smoothness of the approximated inverse. The main advantage of the proposed approach relies on the fact that the series expansion can be computed off-line from simulated data as soon as the experimental configuration is known. Data inversion can then be performed in true real time as soon as the data are acquired. Simulation results are presented in order to show the advantages and limitations of the method. Finally, some inversion results from horizontal towed array data are reported, and are compared with independent estimates of geoacoustic bottom properties.
The behavior of Lamb waves in stressed polymer foils
Authors: Desmet C. , Kawald U. , Mourad A. , Lauriks W. , Thoen J.
Published: October 2005

The influence of externally applied unidirectional stress on the lowest-order Lamb modes of a 12-μm poly(ethylene terephthalate) (PET) film has been investigated both theoretically and experimentally. The Lamb wave dispersion was determined in a fully contactless way by using optical generation and detection of ultrasound. The elastic parameters of the film material were obtained by fitting the angle dependence of the low-frequency limit of the velocity of the fundamental Lamb modes. Whereas the dispersion of the symmetric mode S0 is only slightly influenced by an external stress, the antisymmetric mode A0 shows a transition from dispersion behavior determined by the elastic constants at small stresses to a behavior dominated by the applied stress at large stresses.
Ultrasonic pulsed beam interaction with a fluid-loaded elastic plate: Theory
Authors: Zeroug Smaine , Stanke Fred E.
Published: October 2005

The interaction of transducer-excited ultrasonic pulsed beams with fluid-loaded elastic plates is treated with a computationally efficient analytical model. The model synthesizes the frequency-domain voltage, due to a single transducer operated in reflection (pulse-echo) mode and a pair of tranducers in transmission mode, utilizing an approach that is based on (1) expansion of transducer fields in terms of quasi-Gaussian beams modeled via the complex-source-point technique and its recent extension to finite receivers, and on (2) complex wave-number spectral decomposition and synthesis to solve the beam–structure interaction problem. First, a reference solution for the frequency-domain reflected and transmitted fields is expressed in terms of spectral integrals over two-dimensional infinite spectra of plane waves weighted by the plate reflection or transmission coefficient. Subsequent expansion in terms of a finite sum of integrals representing multiply reflected beams propagating within the plate, combined with high-frequency asymptotics and inverse Fourier transformation of the frequency-domain data, yields the time-domain voltage as a finite sum of purely compressional (P), purely shear (S), and P–S coupled arrivals. Of particular interest is the new higher-order asymptotic expansion developed to account for shear waves excited in the plate by the finite angular spectrum of beams at normal incidence. Both reference and asymptotic solutions have been implemented in numerical codes and validated against experimentally generated data. This is shown in a follow-up paper. The methodology presented here can be applied under more general conditions of transducer orientation and focusing, and also for elastic media with more than one layer.
Effects of spectral smearing on phoneme and word recognition
Authors: Boothroyd Arthur , Mulhearn Bethany , Gong Juan , Ostroff Jodi
Published: October 2005

The principal goal was to measure the effects, on speech perception, of loss of spectral detail in the acoustic signal. Spectral smearing was produced by multiplying the speech waveform by low-pass filtered noise. Performance was measured in normal adults as the percentage of phonemes correctly repeated in lists of monosyllabic words. A smearing bandwidth of 250 Hz (i.e., each tonal component of the instantaneous spectrum replaced by a 250-Hz band of noise) had a small but significant effect on phoneme recognition. A smearing bandwidth of 8000 Hz was required to reduce phoneme recognition to a value that was indistinguishable from that produced by complete smearing. Vowels were somewhat more susceptible to the effects of spectral smearing than were consonants, and initial consonants were more susceptible than were final consonants. In an analysis of errors, place of consonant articulation was more susceptible than either manner of articulation or voicing. These findings are attributable to differences in the relative importance of spectral and temporal cues. Word recognition was more susceptible to the effects of spectral smearing than was phoneme recognition, but this finding was predictable on the basis of the known nonlinear relationship between the two measures. In a second experiment, smearing bandwidths of 707 and 2000 Hz increased phoneme recognition threshold by 12.9 and 16.4 dB, respectively, compared to that found without smearing. (Phoneme recognition threshold is defined, here, as the signal-to-noise ratio at which phoneme recognition is 50% of the value obtained in quiet.) The data are consistent with the hypothesis that reduced spectral resolution affects phoneme recognition to the extent that it reduces access to the formant patterns in the spectral envelope.
Accurate recovery of articulator positions from acoustics: New conclusions based on human data
Authors: Hogden John , Lofqvist Anders , Gracco Vince , Zlokarnik Igor , Rubin Philip , Saltzman Elliot
Published: October 2005

Vocal tract models are often used to study the problem of mapping from the acoustic transfer function to the vocal tract area function (inverse mapping). Unfortunately, results based on vocal tract models are strongly affected by the assumptions underlying the models. In this study, the mapping from acoustics (digitized speech samples) to articulation (measurements of the positions of receiver coils placed on the tongue, jaw, and lips) is examined using human data from a single speaker: Simultaneous acoustic and articulator measurements made for vowel-to-vowel transitions, /g/ closures, and transitions into and out of /g/ closures. Articulator positions were measured using an EMMA system to track coils placed on the lips, jaw, and tongue. Using these data, look-up tables were created that allow articulator positions to be estimated from acoustic signals. On a data set not used for making look-up tables, correlations between estimated and actual coil positions of around 94% and root-mean-squared errors around 2 mm are common for coils on the tongue. An error source evaluation shows that estimating articulator positions from quantized acoustics gives root-mean-squared errors that are typically less than 1 mm greater than the errors that would be obtained from quantizing the articulator positions themselves. This study agrees with and extends previous studies of human data by showing that for the data studied, speech acoustics can be used to accurately recover articulator positions.