bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of finite-difference and fast-field modeling
Authors: Ro/sten Tage , Amundsen Lasse , Arntsen Bo/rge , Kristensen Åge
Published: October 2005

The finite-difference technique is used to model Scholte wave propagation excited by a P-wave source in the water layer. The finite-difference approach encompasses models in which the parameters are allowed to vary with position both vertically and laterally, and is well suited for studies of the acoustic field at and below the seafloor. The finite-difference algorithm implemented is a 2-D acceleration-stress staggered grid scheme, of second order in time and order 2L in space. The formulation results in a simple numerical implementation of irregular liquid–solid interfaces. To investigate numerical issues which require special attention when implementing finite-difference schemes, the finite-different seismograms are compared with seismograms modeled by a fast-field technique valid for range-independent models. In particular, the methods are compared for models containing sharp liquid–solid interfaces representative of the seafloor. Numerical analysis indicates that the liquid–solid interface is located in a transition zone between fundamental finite-difference cells of constant parameters of liquid and solid. Excellent agreement with the transform technique is demonstrated.
Using surface waves to detect a point diffractor buried at the sea bottom
Authors: Kristensen Åge , Mittet Rune
Published: October 2005

Shallow-water mine counter measurement is difficult due to high noise levels, a complex environment, and a low-frequency cutoff for waterborne modes. However, interface waves may be used as a probe since they have no cutoff frequency. Further advantages are that interface waves have less geometrical spreading than volume waves. A high-order 3-D elastic finite-difference scheme is used to solve the problem. With a sloping seafloor and the mine included, there are no simplifying symmetries. At low frequencies, approximately 30 Hz, a mine can be represented as a point diffractor. The mine is assumed to be buried just below the seabottom interface. The detectors are geophones on the seafloor and on the beach. The potential for interface waves (Scholte and Rayleigh waves) excited by a source and scattered by a mine to be detected at the geophone locations has been investigated. Several experimental configurations are analyzed with the source located in the water, on the seafloor, and on the beach. Calculations have been performed with variations in the physical properties of the mine. A force source on the seafloor or beach gives results which are easier to interpret than for a volume source in the water layer. For realistic physical properties of a plastic mine the backscattered signal was found to be −60 dB compared to the outgoing signal.
Measurements of seabed damping coefficients from head waves in shallow water
Authors: Hall Marshall V.
Published: October 2005

Acoustic signals from small explosive charges have been measured with sonobuoys on several tracks in shallow water. Using the frequency band from 14 to 70 Hz, travel times of head waves were monitored, and the sound speeds and depths of corresponding interfaces in the seabed were derived. Head waves from interfaces indistinguishable from the seafloor (the water/seabed interface) were detected on only two of the tracks, with sound speeds around 2300 m/s. The amount of data obtained for the seafloor was limited by incoherence of the signals and, for some tracks, by inappropriate experimental method. Range dependencies of head wave energy in the 25-Hz third-octave band were measured on four tracks whose seafloor depths ranged from 60 to 100 m. These interfaces were between 0 and 220 m beneath the seafloor, and their sound speeds ranged between 2000 and 2400 m/s. Results for damping coefficient range from 0.4 to 0.8 dB/cycle, with standard errors of around 0.1 dB/cycle. Damping in the deepest interface (whose sound speed was 2200 m/s) was measured at six frequencies from 16 to 63 Hz, and over this band there is a weak tendency for the damping per cycle to decrease with frequency.
The bidirectional reflectance distribution function of an ocean ridge
Authors: Makris Nicholas C. , Fialkowski Laurie T.
Published: October 2005

The bidirectional reflectance distribution function (BRDF) of a typical highly lineated deep-ocean ridge on the western flank of the Mid-Atlantic Ridge is estimated by applying classical radiometric theory to long-range bistatic reverberation measurements obtained during the ARSRP Main Acoustics Experiment of 1993. The BRDF of a surface is defined as the ratio of the reflected radiance toward the direction of the receiver to the irradiance in the direction toward the source. Therefore, such effects as two-way transmission loss, the areal resolution of the measurement, and its foreshortening are accounted for in computation of the BRDF. (For example, the BRDF for a Lambertian surface is simply 1/π.) In particular, high-resolution bathymetry of 5-m resolution, roughly the scale of the acoustic wavelength for the low-frequency measurements, is used to determine surface orientation and foreshortening. The parabolic equation is used to compute two-way transmission; a ray trace is used to determine incident and scattered angles at the surface; and a spatial convolution is used to account for the spatially varying areal resolution of the measurement system. Statistical fluctuations due to nonlinear speckle noise inherent in the measurements are reduced by stationary averaging and are stabilized by logarithmic transformation.
Finite-amplitude sound wave propagation in granular marine sediment with fractal structure
Authors: Esipov Igor B. , Matveev Konstantin I. , Naugolnykh Konstantin A.
Published: October 2005

The wave energy localization in the process of sound propagation in the media with fractal structure leads to the frequency dependence of the nonlinear response. In the low-frequency range, a sound wave, propagated through the water-saturated granular matter, has a typical attenuation, related to the Biot theory. In the range of fractal structure, spatial scales oscillations occur as localized ones. This state of oscillations is known as fractons. The appropriate spectrum of oscillations is related to the fractal dimension of the studied media and falls drastically with the frequency. Experiments of finite-amplitude, wide frequency sound pulse propagation through the sample of cobalt–manganese crust deposits are analyzed with respect to appropriate computer-simulated models. Abnormally large sound attenuation at relatively small-amplitude signal propagation in the frequency range up 0.7 MHz, was shown, while at the large signal amplitude, the value of the signal attenuation falls and reaches the Biot frequency pattern. [Work supported by the Russian Basic Research Foundation, Grant No. 95-02-06353.]
Temporal fluctuations of scattered field due to bioturbation in marine sediments
Authors: Jones Christopher D. , Jackson Darrell R.
Published: October 2005

Biological activity in marine sediment creates a time-varying, randomly fluctuating medium. A bio-diffusive sediment model is proposed for density and sound-speed fluctuations within the sediment. Using perturbation theory to model sediment volume scattering, the decorrelation of the scattered field due to biological activity can be predicted. This decorrelation can be estimated from field data by comparing seafloor backscatter from the same location at different times. By fitting the model to such data, sediment bio-diffusion constants can be estimated. Such acoustically inferred values of sediment bio-diffusion are compared with directly measured values. [Work supported by ONR.]
Technical issues related to sound power measurement standards
Authors: Maling George C. , Nobile Matthew A.
Published: October 2005

As the ‘‘3740 series’’ of International Standards on Sound Power Determination are revised, several technical issues must be considered. In ISO 3745, the characteristics of the sound source used to qualify a hemi-anechoic room for precision measurements must be carefully considered. The use of a low-profile source placed just above the floor of the room, and the performance of the same source in the plane of the floor are described. The discrete microphone positions used on a hemispherical measurement surface must also be carefully studied and perhaps changed. Experience with ISO 6926 shows that an array of microphones having discrete positions have ‘‘holes’’ in their frequency response, and optimization of this response is critical. In ISO 3741, the method used to determine the minimum distance between the source and the microphones must be carefully studied, especially at high frequencies. The qualification procedure for reverberation rooms in ISO 3742 must also be examined with a view toward the use of modern instrumentation and speed of performing room qualification. The use of special test signals matched to the characteristics of a particular analyzer is considered.
Sound power determination method for large-scale sound sources
Authors: Kamata Minoru , Yamazaki Toru , Ikeda Hideo , Baba Nobuhiro
Published: October 2005

Recently, the accuracy of sound power measurements during the actual operation of a machine in situ improved by using sound-intensity measuring technology. The standard measuring method is being established at ISO. However, one has much difficulty in measuring the sound intensity of large-scale sound sources because the measurement becomes time consuming. On the other hand, there is a simple survey method based on sound-pressure measurements. However, accurate evaluation of the environmental correction factor is then difficult. Based on this background, this paper describes the sound power determination method for large-scale sound sources. Sound intensity measurements were carried out on several large marine diesel engines, which were installed in the ship’s engine room or on the manufacturer’s test bed where the sound condition was far from free field. Accuracy of the sound power evaluation in such conditions and practicality of the intensity measurement are discussed by detailed analysis of the measured data. Furthermore, a new convenient method called the hybrid method, which is based on the sound-pressure method but needs several points of intensity measurement, is proposed and its practical merit is discussed.
Energy flow and intensity flux in sound fields
Authors: Tichy Jiri
Published: October 2005

The radiation and propagation of sound energy is represented by time-dependent instantaneous intensity. The concept of sound energy particles and their trajectories is discussed. The time-averaged flux of acoustic energy is represented by acoustic intensity. When measuring sound power radiation the knowledge of intensity fields is important for the selection of measurement points to achieve the desired precision of sound power determination. The near-field intensity of typical sound radiators is shown and the issues of sound power measurements are discussed.
Characterization of a removable, hemianechoic floor in Health Canada’s large anechoic chamber
Authors: Keith S. E.
Published: October 2005

Health Canada is interested in promoting the use of quieter industrial machinery through sound power measurement and labeling. To measure sound power under standard hemianechoic conditions, a removable floor was installed and tested in the anechoic chamber. The floor had dimensions 13 m× 9 m and was constructed from 2.8-cm-thick concrete tiles. It was designed to have a sound absorption coefficient below 0.06 in the range 50 Hz–20 kHz, as required by sound power measurement standards. Characterization of the acoustical performance using ISO3745 indicated that measurements were acceptable to a distance of more than 2 m. In situ estimates of the absorption coefficient using acoustic intensity showed the local absorption coefficient could be improved by sealing the joints in the floor. The intensity technique also showed that below 125 Hz, the absorption coefficient was limited by the floor dimensions. In situ vibration measurements of individual floor tiles suggested that the absorption coefficient was acceptable under acoustical excitation. Floor vibration and reradiation of sound power can be a problem in any room. Calculation of sound power radiated from the floor using vibration measurements (ISO/TR7849) was found useful for determining if a source should be vibration isolated.
Studies on sound and vibration generated by household appliances. II. The determination of vibromotive force of waste disposers by a comparison method
Authors: Kaite Masahiro , Ohkawa Heiichiro , Koyasu Masaru
Published: October 2005

The household food waste disposer is attracting attention as one of the leading disposal systems in Japan, and it is thought that disposers will be installed in many condominiums from now on. Sound and vibration which are generated by a disposer will come under fire as a new noise source. To popularize the disposer in Japan, reduction of the sound and vibration which are generated by disposers is an important matter. In this paper, as a standard method for measurement and evaluation of the vibration which is generated by disposers, the determination of the vibromotive force level of disposers is studied by the comparison method. As a result, it is clear that the vibromotive force level of a disposer is influenced by the kinds of food waste, but the frequency characteristic is relatively unaffected, a behavior similar to that found for sound power level.
Sound power determination using sound intensity: A review of the technique and the ISO 9614/1 standard
Authors: Barrera-Figueroa Salvador , Nightingale Trevor
Published: October 2005

The sound power emitted by a source with a highly directional behavior was determined using sound intensity measurements. The parameters varied were: number of measurement points, degree of reactivity of the measurement room, level of extraneous noise, shape of the measurement surface, and distance from source to measurement surface. Both the ISO field indicators and ISO criteria were examined. The relation between the changes in the ISO indicators and criteria and the accuracy obtained was studied. It was found that, for most of the cases, the requirements due to the values taken by ISO criteria did not have a correlation with the accuracy obtained in the measurement, especially those values of ISO criterion 2 (related to the statistical distribution of measured intensity). The statistical nature of this criterion is not the best way to indicate the accuracy of a sound power determination. Also, criterion 2 fails when there is an extraneous noise source. The influence of environment reactivity was found to be a limitation on the accuracy of the technique. The results obtained coincide with those obtained by various researchers around the world. [Work supported by the National Center of Metrology, México, and the Acoustics Laboratory of IRC-NRC, Canada.]
Resolving the moment of collapse of a sonoluminescing bubble
Authors: Weninger Keith , Putterman S. J. , Barber B. P.
Published: October 2005

Femtosecond pulsed Mie scattering and a needle hydrophone have been used to probe the behavior of a light-emitting bubble near that moment when the stress of implosion is at a maximum. It is found that the wall of the bubble is collapsing with a velocity over four times the ambient speed of sound in the gas. The deceleration at the minimum is over 1011 g. The improved timing resolution afforded by this arrangement localizes the flash to within 500 ps of the minimum. The collapsing bubble launches a strong pulse into the surrounding water with a rise time shorter than 10 ns. [Work supported by the NSF.]
Modification of bubble properties by direct injection of insoluble surfactants and other advances in bubble dynamics
Authors: Thiessen David B. , Marston Philip L. , Asaki Thomas J.
Published: October 2005

Direct injection of a submicroliter ethanol solution of insoluble surfactant onto the surface of levitated or pendant bubbles in water facilitates the spreading of a known monolayer coverage on the surface of a bubble. As the bubble dissolves, its surface area decreases and the monolayer is compressed. This method has facilitated the measurement of the evolution of the damping of capillary oscillations [Asaki et al., Phys. Rev. Lett. 75, 2686–2689 (1995); 75, 4336(E) (1995)]. It has also been used to obtain direct measurements of the film pressure as a function of coverage for pendant bubbles. To investigate the effect on radial pulsations, new methods of monitoring the radial response of a bubble would be desirable. A novel method of exciting the radial pulsations of bubbles in oil will be described [Marstonet al., J. Acoust. Soc. Am. 99, 2560(A) (1996)] based on dielectrophoretic levitation and modulation of the Maxwell stress of an applied electric field. [Work supported by the Office of Naval Research.]
Application of implosion to underwater sound generation
Authors: Yen Nai-chyuan
Published: October 2005

This paper addresses the possible utilization of a highly concentrated pressure pulse caused by an implosion mechanism, as an underwater sound source. The operation principle and character of the uncontrolled implosion sound sources currently used in the underwater community, devices such as crushing light bulbs for sound propagation measurements and water guns for oil exploration, will be reviewed. Based on recent research efforts aimed at the understanding of the sonoluminescence phenomenon and a physical model for the collapse of a bubble, analytic results were employed to investigate the controllability of implosion for underwater sound generation. This includes the designing of an artificial cavity other than a sphere, initiating a shock wave and reshaping it for spherical convergence, manipulating the fluid–vapor composition in relation to the pulse signature, and assessing the conversion of hydrodynamic energy to acoustic energy. Some test data derived from prototype measurements in the laboratory and computer simulations will be used to discuss the feasibility of developing a simple, safe but controllable, implosion sound projector to meet practical needs in the underwater community.
The effects of surfactant additives on the acoustic and light emissions from a single stable sonoluminescing bubble
Authors: Stottlemyer Thomas R. , Apfel Robert E.
Published: October 2005

The localization concentration of energy during a single bubble collapse is manifested in two forms, which are the emission of an acoustic pulse, and the emission of a light pulse. Through the precise control of experimental parameters, one can levitate a single bubble in a standing wave field and measure the magnitude of the acoustic and light pulses resulting from the violent collapse of the cavity. An experimental apparatus was developed to measure the acoustic and light emissions from a single, stable sonoluminescing bubble. Two surfactant additives were studied to determine the effects on the bubble emissions. Triton X-100, which has previously been shown to provide free interfacial motion, reduced the magnitude of both the acoustic and light pulses from the bubble. The protein bovine serum albumin (BSA), which has been shown to hinder interfacial motion, allowed the bubble to be driven to higher acoustic pressures and resulted in an increase in the magnitude of the light pulses from the bubble. Images of the sonoluminescing bubble indicate that the collapse remains spherical in the cases presented, and that bubble translation can be correlated with weak acoustic and light emissions.
Apparatus for obtaining a high-resolution optical spectrum of sonoluminescence
Authors: Hiller Robert A. , Putterman S. J.
Published: October 2005

The region of light emission in a sonoluminescing bubble is so stressed that the spectrum is mostly ultraviolet and spectral lines are not apparent at the level of resolution currently employed (10 nm FWHM). In order to increase resolution and search for possible structure within the broadband spectrum, a new apparatus which makes use of reflection optics has been developed. [Work supported by the NSF.]
Measurements of the acoustic emission from glowing bubbles
Authors: Hallaj Ibrahim M. , Matula Thomas J. , Roy Ronald A. , Crum Larry A.
Published: October 2005

A single bubble trapped in an acoustic standing wave can be made to undergo highly nonlinear volume mode pulsations resulting in inertial cavitation—the expansive growth and violent collapse of bubbles. Under certain conditions the collapse results in light emission called sonoluminescence (SL). Though much has been studied regarding properties of the emitted light, little work has been done on the acoustic emission from such a bubble. Previous measurements [Cordry et al., J. Acoust. Soc. Am. 98, 2921(A) (1995)] using a needle hydrophone show only a general low-level acoustic signature. In the present study, a broadband, nonfocused transducer is used to record the acoustic emission from single bubbles at various acoustic drive amplitudes in the SL and non-SL producing regions. The typical acoustic signature includes a large amplitude pulse corresponding to the initial collapse followed by smaller amplitude pulses corresponding to the rebounds. The rebounding bubble essentially oscillates at its resonance frequency so that the simple measurement of the time interval between rebounds makes it relatively easy to measure one of the fundamental unknowns of a sonoluminescence bubble—its equilibrium radius. [Work supported by NSF and ONR.]
Preliminary experimental observations of the effects of buoyancy on single-bubble sonoluminescence in microgravity and hypergravity
Authors: Matula Thomas J. , Roy Ronald A. , Crum Larry A. , Kuhns David L.
Published: October 2005

The buoyancy force [given by the product of the density of the liquid, the gravitational constant, and the volume, ρgV(t)] may play an important role in the stability of small bubbles undergoing highly nonlinear radial pulsations. In particular, during a single acoustic cycle, a sonoluminescence bubble undergoes volume changes on the order of 1000, and thus the buoyancy force changes by this same factor. Since the equilibrium position of such a bubble in a standing wave is balanced by the Bjerknes and buoyancy forces, the bubble may be subjected to large translational velocities and accelerations during each acoustic cycle [S. M. Cordry, Ph.D. thesis, U. M. (1995) and J. Acoust. Soc. Am. 97, 3375 (1995)]. The buoyancy-force stability issue was examined in a series of experiments aboard a NASA KC-135A, which performs parabolic maneuvers to generate limited periods of microgravity. Effects were examined in both microgravity and hypergravity (≊ 0 and 2 g, respectively). Results of this study, performed in November 1995 in the Netherlands, under the auspices of the European Space Agency, will be presented. [Work supported by NSF, CPAC, NASA, and ESA.]
The segregation of frequency-modulated concurrent harmonic sounds
Authors: de Cheveigné Alain , Marin Cécile
Published: October 2005

Recent studies failed to find effects of frequency modulation (FM) on the segregation of concurrent harmonic sounds, beyond those imputed to induced differences in instantaneous fundamental frequency (F0). This study renews the attempt using a paradigm designed to be sensitive to segregation schemes involving FM. Subjects were presented with stimuli consisting of single vowels (a, e, i, o, u) or pairs of concurrent vowels. Vowels within a pair were different. Mean F0s were either the same or differed by 6%. F0s were either constant, or modulated by an ‘‘n’’- or ‘‘u’’-shaped cosine waveform. Levels differed by 15 dB to reduce ceiling effects for the weaker vowel and enhance sensitivity. Stimulus duration was 250 ms. The number of vowels reported per stimulus and the identification rate of the weaker vowel were recorded for each condition. Both were greater for conditions that differed in F0 than at unison, but they were not affected by the modulation state of the target (weaker vowel) or the background (stronger vowel). Additional conditions were tested in which both vowels were inharmonic, on the assumption that FM might enhance the fusion of their components. Again no effect of FM was found.
Attentional filter of a multiple-component tone
Authors: Miyazono Hiromitsu , Takao Kenji , Usagawa Tsuyoshi , Ebata Masanao
Published: October 2005

When listeners focus on a sound with two or more frequency components to detect an auditory signal, other unattended sounds are suppressed and sensitivity to those sounds is diminished. This result suggests that an attentional filter is involved in the auditory processing. This study shows how to detect the various frequencies when attention is directed by a multiple-component tone. Two components and a number of harmonic tones are presented as a cue signal in the probe-signal procedure. When the cue tone has two components, the target tone is a signal with and near a component frequency. In the case of a harmonic cue, it is a signal with a component, with and near a fundamental frequency. Using ROEX filter estimation, the bandwidth of the attentional filter is discussed. As a result, the frequency spacing between two components affects the shape of the attentional filter. The bandwidth of a filter is almost equal to the critical bandwidth, when the components are moderately apart. Meanwhile, when very far apart, the bandwidth is larger than the critical one. When the cue is a harmonic signal, the detectability of the component signal is less than that with a fundamental frequency. The asymmetric filter is estimated in a fundamental frequency.
The representation of auditory source characteristics: Simple geometric form
Authors: Lakatos Stephen , McAdams Stephen , Causse Rene
Published: October 2005

Two experiments examined listeners’ ability to discriminate the geometric shape of simple resonating bodies on the basis of their corresponding auditory attributes. In cross-modal matching tasks, subjects listened to recordings of pairs of metal bars (experiment 1) or wooden bars (experiment 2) struck in sequence, and then selected a visual depiction of the bar cross sections that correctly represented their relative widths and heights from two opposing pairs presented on a computer screen. Multidimensional scaling solutions derived from matching scores for metal and wooden bars indicated that subjects’ performance varied directly with increasing differences in the width–height ratios of both sets of bars. Subsequent acoustic analyses revealed that the frequency components from torsional vibrational modes and the ratios of frequencies of transverse bending modes in the bars correlated strongly with both of the bars’ width–height ratios and bar coordinates in the multidimensional configurations. The results suggest that listeners can encode the auditory properties of sound sources by extracting certain invariant physical characteristics of their gross geometric properties from their acoustic behavior. [Work supported by CNRS.]
Selective weighting of signal information in auditory discrimination tasks
Authors: Bailey Peter J. , Hill Nicholas I.
Published: October 2005

Listeners can detect a weak tonal signal in noise more successfully when the signal is at an expected frequency than when the signal frequency is unexpected [e.g., Dai et al., J. Acoust. Soc. Am. 89, 2837–2842 (1991)], suggesting that listeners focus their attention on frequency regions where distinctive information is likely to be found. This ability may benefit listeners faced with the task of discriminating natural sounds in noisy environments. However, demonstrations of selective weighting of acoustic information in discrimination tasks are relatively few. Results will be reported of an experiment in which subjects were required to discriminate two complex tones consisting of seven equal-amplitude components. The tones were distinguished by an increment in the amplitude of a single spectral component. When the increment was added to an expected component, discrimination performance was better than when an unexpected component was incremented. A similar result was found in a second experiment in which the levels of all spectral components were randomized between each trial. The relatively better discrimination performance shown for expected discriminanda is interpreted as an effect of attention directed by expectation to the spectral region encompassing the incremented component. [Work supported by UK MRC.]
Temporal integration mechanisms for complex tones consisting of unresolved harmonics
Authors: White Louise J.
Published: October 2005

There is a large effect of duration on fundamental frequency (F0) discrimination for complex tones consisting of harmonics unresolved by the peripheral auditory system [C. J. Plack and R. P. Carlyon, J. Acoust. Soc. Am. 98, 1355–1364 (1995)]. The present experiment investigated the mechanisms underlying this effect by measuring F0 discrimination for complexes of unresolved harmonics with continuous durations between 20 and 160 ms and for pairs of 20-ms unresolved complexes separated by a silent interval of between 5 and 80 ms. For the continuous signals, d′ increased by a factor of 2.4 between the 20-ms signal and the 40-ms signal. For the paired signals d′ increased relative to the 20-ms signal by a factor between 1.2 and 1.6, independent of the silent interval duration. This increase is similar to that predicted by signal detection theory. These data support the hypothesis that the pitch mechanism for unresolved harmonics can use a long integration window for continuous signals but reverts to a ‘‘multiple looks’’ mechanism, involving the efficient combination of discrete short-duration samples, when there is some discontinuity in the signal. [Work supported by MRC (UK).]
Pitch and pitch strength of iterated rippled noise: Is it the envelope or fine structure?
Authors: Yost William A.
Published: October 2005

Iterated rippled noise (IRN) stimuli are generated by a cascade of delay and add networks; where delay, gain after delay, and number of iterations of delay and add are the variables controlling IRN stimuli. IRN stimuli produce a sound with a tonal and a noisy percept. The tonal component is related to regularity in the stimulus and the noisy component is related to a lack of regularity. Autocorrelation is a useful measure for describing the degree of regularity in IRN stimuli. However, the envelope of IRN stimuli also has a regular and an irregular structure that can be revealed by autocorrelation. Thus, the perception of IRN stimuli could be based on fine structure and/or envelope. Autocorrelation based on fine structure is different when the delayed noise is subtracted (gain<0) than when it is added (gain≳0) to the undelayed noise. However, the autocorrelation function for the envelope is the same for both addition and subtraction. Discrimination between IRN stimuli generated with addition and subtraction as a function of highpass filtering suggests that processing of IRN stimuli is based on fine structure. [Work supported by NIDCD.]
Is power equipartitioned in complicated structures?
Authors: Dyer Ira
Published: October 2005

A tenet of statistical energy analysis is that power of an elastic wave is partitioned equally among the substructures of an overall structure, and prevails when modes of each overlap those of the other substructures. Is power equipartition achieved for all complicated structures, specifically, for those in which several wave types spatially coexist? Recent research equivocates: only sometimes! Analysis by He for a finite-length ringed shell in water shows power equipartition among compressional, shear, and flexural waves. But measurements by Machens and Dyer, and by Bondaryk, on various 3-D truss structures in air, do not show power equipartition. An explanation for the apparent contradiction in these different structural systems is not, at this writing, worked out. Speculations, however, point to the differences between scattering from one wave type to another, on the shell and in the truss. On the shell, scattering at a ring is distributed with finite width in helical angle. In the truss, scattering is localized at truss joints. Both systems have spatial regularity and hence stopbands, but the helical angle width on the shell can induce good wave–wave spatial overlap, while no ‘‘extra’’ dimension is available in the truss to counter the stopband rejections. [Supported by ONR.]
Effect of internal oscillators on the acoustic response of a ribbed shell
Authors: Photiadis Douglas M. , Houston B. H. , Bucaro J. A.
Published: October 2005

The response of a ribbed shell with many attached internal oscillators to a point force has been measured by near-field acoustic holography and compared to similar measurements of a ribbed shell with no oscillators. The total mass of the attached oscillators is significant, of order of the mass of the ribbed shell. The measurements show that the internal attachments have a very significant and complex impact both on the local response of the shell and on the propagation of vibration along the shell. At low frequencies the range of propagation is reduced, consistent with an increase in the effective ‘‘damping,’’ while at high frequencies, the range of propagation is increased. Examination of the input impedance of the system reveals a frequency dependence consistent with this behavior. These observations and their implications on the underlying scattering and absorption mechanisms resulting from the internal structure will be discussed.
Scattering from a submerged shell with many internal oscillators
Authors: Bucaro J. A. , Houston B. H. , Photiadis Douglas M.
Published: October 2005

The measured scattering of sound from a submerged, framed shell was considered in whose interior have been attached hundreds of precisely tuned and pseudorandomly distributed mechanical ‘‘dumbell’’ oscillators. The dumbells are attached to the frames at the formers’ beam midpoints, with the beams canted at 45 deg to the frame web direction. It is assumed that, for the most part, the motion of the frames couples directly to beam-bending motion of the dumbell oscillators, the degree of freedom considered in the design of the oscillator resonant frequencies. The observed scattering—both in frequency and aspect—is quite different from that observed from the framed shell without any such oscillators. These differences are discussed in the context of membrane and flexural shell waves, the coupled frame–oscillator systems, and related mechanisms that might account for the observed scattering features. [Work supported in part by ONR Code 334.]
Observation of membrane and flexural modes on a cylindrical shell
Authors: Manning Patricia A. , Bondaryk Joseph E.
Published: October 2005

A test facility has been set up in the MIT Acoustics & Vibrations Laboratory with the intent of studying various modifications to shell structures which would facilitate control of membrane waves. Previous research on finite-length submerged shells has shown the importance of membrane waves in the mid-frequency, high aspect angle regimes. These shear and compressional waves are important because they are the principle determinants of the shell’s radiation and scattering properties. Flexural waves are poorly coupled to the acoustic medium (water), so they serve mainly as modifiers of the membrane waves. MIT’s preliminary test structure consists of a thin steel shell with conical endcaps. An axisymmetric source array is used to generate single modes and the resulting accelerations are measured with an axial line array. Array processing is used to separate the measured accelerations into the three wave types. Data showing shear, compressional, and flexural modes in both forward and backward propagation directions has been collected. Strong coupling between flexural modes was observed in the data, probably due to an axial weld seam along the length of the shell. The experimental dispersion curves closely match theoretical predictions. [Research sponsored by ONR.]
Vibration of periodic truss structures
Authors: Bondaryk Joseph E.
Published: October 2005

Recent trends in underwater vehicle design suggest the use of truss-like structures, connected to the hull by a limited number of attachment points, to support vibrating machinery. This work investigates the dynamic behavior of a set of spatially periodic trusses of practical interest. As expected, experimental and numerical modeling shows that this periodicity causes the trusses to behave as mechanical comb filters in frequency. However, the multiple periodicities at work in the truss and impedance discontinuities at the truss joints cause the resonant peaks at low frequencies to widen significantly. The consequence of this effect suggests that trusses with varied strut lengths tend to a low-pass characteristic. This is confirmed by data from a truss with several strut lengths. [Research supported by ARPA and ONR.]
Wave transmission along a ribbed fluid-loaded membrane
Authors: Cook Paul D. , Spivack Mark
Published: October 2005

This work studies wave transmission along a fluid-loaded membrane supported by an array of ribs, one of which is driven harmonically. The influence of realistic rib dynamics is considered, including finite mechanical impedance as well as spring and damping forces. Under heavy fluid loading, when the coupling between ribs is dominated by the surface wavefield in the fluid, the system exhibits the usual stop/pass band structure. It is shown that there exists a critical rib mass, depending on drive frequency, at which the disturbance becomes completely localized at the driven rib. For frequencies at a band edge, the solution at the critical mass is no longer unique; in this parameter region, the solution is highly sensitive to small changes in frequency or rib properties. Varying the parameters in different ways gives rise to different limiting behavior at the critical points. Numerical simulations have been carried out to study this system. These simulations confirm the analytical predictions and help to determine when the surface wave approximation breaks down.
Transient response of coupled modes in complex structures
Authors: DeJong Richard G.
Published: October 2005

The transient response of coupled modes is considered. Numerical and experimental results are presented for resonators, beams, and plates subjected to impulsive and random excitations. Using a random vibration analysis the time constant of response for a resonator is found to be inversely proportional to the damping bandwidth. Using a transient SEA formulation the time constant for a modal response is found to be inversely proportional to the modal bandwidth which includes the effects of both the damping and coupling loss factors.
Nondestructive estimation of the position of a crack in a concrete block by eliminating the effect of surface waves
Authors: Abe Masato
Published: October 2005

This paper describes a method for estimating, using many sensors, the position of a crack in a concrete block, most of which is buried in the ground. An array of sensors is attached on the surface of the concrete block, and a vibration pulse is forced using a small hammer. Since the forced vibration reflects at the position of a crack, it may seem that the position can be easily estimated by picking up the reflection wave with an array of sensors and by analyzing the received signals using a beamforming technique. It is difficult, however, to estimate the position since the magnitude of the surface wave is much greater than that of the reflection from the crack and there are many reflection waves from the boundaries of the concrete block. Therefore, this paper proposes a method to eliminate not only the effect of the surface wave but also that of the reflection waves from the sidewalls and/or bottom, and extracts the necessary reflections (primary and secondary waves) from a crack. The position of the crack is estimated using the extracted waves by a beamforming technique.
Localized modes in a nonlinear system
Authors: Abramian A. K. , Vakulenko S. A.
Published: October 2005

It is shown that there exist a large class of nonlinear elastic systems (which includes both dissipative and conservative systems) where localized modes (linear or nonlinear) completely define the large time behavior. For dissipative systems, there are possible generations of unboundedly complicated chaotic attractors. For some conservative (for example, weakly nonlinear) elastic systems, the method developed allows one to construct an algorithm of the integration of the corresponding evolution equations. The phenomenon of vibration and nonstationary wave localization within beams, plates, and shells has been studied using the nonlinear approach.
Prediction of foreign-accented speech intelligibility from segmental contrast measures
Authors: Rogers Catherine L. , Dalby Jonathan M.
Published: October 2005

The intelligibility of foreign-accented English was investigated using minimal-pairs contrasts probing a number of different error types. Forty-four native English-speaking listeners were presented with English words, sentences, and a brief passage produced by one of eight native speakers of Mandarin Chinese or one native English speaker. The 190 words were presented to listeners in a minimal-pairs forced-choice task. For the sentences and passage, listeners were instructed to write down what they understood. A feature-based analysis of the minimal-pairs data was performed, with percent correct scores computed for each feature. The sentence and passage data, scored as percent of content words correctly transcribed by listeners, were transformed and used as the dependent variables in two multiple regression analyses, with seven feature scores from the minimal-pairs test (four consonant and three vowel features) used as the independent variables. The seven minimal-pairs variables accounted for approximately 72% of the variance in sentence intelligibility and 49% of that of the passages. Of these seven variables, vowel tenseness, diphthongization, and consonant voicing accounted for 70% of the sentence and 45% of the passage variance. These data suggest that specific segmental error types may have differential effects on intelligibility. [Work supported by NIH-NIDCD Grant No. 2R44DC02213.]
Cue weighting for American English /r/ and /l/ by 7.5-month-old infants
Authors: Iverson Paul , Kuhl Patricia K.
Published: October 2005

Recent research on American English /r/ and /l/ has suggested that adult Japanese speakers are more sensitive to changes in F2 frequency than to changes in F3 frequency. In contrast, adult American English speakers seem more sensitive to changes in F3 frequency. To examine the developmental origins of these cue weightings, 7.5-month-old infants raised in monolingual English homes were tested. Following the head-turn conditioning procedure, infants were trained to turn toward a visual reinforcer whenever a continuously repeated background stimulus was changed to a test stimulus. In an initial conditioning phase, infants were trained to discriminate two synthetic /ra/ and /la/ stimuli that differed in both F2 and F3. In the following test phase, infants discriminated these two stimuli along with stimuli that differed from the background along only one of these dimensions. The results demonstrated that infants were more sensitive toF 2 than to F3, suggesting that their cue weightings may better match those of Japanese adults.
Language-specific timing of infant voice onset in response to maternal vocal priming
Authors: Anderson Samuel W.
Published: October 2005

Recent studies have found that infants show early sensitivity to the characteristic metric structure of the primary language to which they are exposed, and do so long before they acquire the ability to generate speech itself [A. Cutler and J. Mehler, J. Phon. 21, 103–108 (1993); A. Cutler, Cognition 50, 79–81 (1994)]. Vocal exchanges between 30 mothers and their 4-month-old infants were recorded during 10 min of spontaneous face-to-face play. Vocalizations were digitized in 123-ms units, yielding a preliminary result: 27 out of the 30 infants began vocalizing more often at times when maternal speech was already underway (priming) than when the mother was silent. In the present analysis, vocalization distributions are fitted modulo 395 ms—the mean duration of syllabic stress groups in American English. The investigation examines whether infant coactive onsets occur systematically near stress group boundaries or randomly throughout, and, if systematic, whether the infant’s tendency to respond metrically varies according to the length of the mother’s preceding utterance. Also examined is whether either the mother’s speech and/or the infant’s onset distribution may be less systematic in the three cases where priming was rare. [Collaboration of Dr. Beatrice Beebe and Dr. Joseph Jaffe is acknowledged.]
The perception of morae in long vowels: Comparison among Japanese, Korean, and English speakers
Authors: Omuro Kaori , Baba Ryoji , Miyazono Hiromitsu , Usagawa Tsuyoshi , Egawa Yuichi
Published: October 2005

It is well known that there are three kinds of Tokushuhaku (the specific timing morae) in the Japanese language such as the moraic nasal, the non-nasal consonant, and the long vowel. Even though Japanese native speakers can perceive them perfectly, it is difficult for Japanese learners from abroad to perceive and acquire them. To make it more efficient for Japanese learners to acquire them, how Japanese native speakers perceive Tokushuhaku needs to be investigated. This study examines the perception of a mora or morae specifically in the long vowel. Previously it has been assumed that duration contrasts along are involved in perception of native Japanese speakers. However it is hypothesized that the accentual change plays an important role for the perception of morae. Based on the hypothesis perception tests with computer-edited sound, stimuli were given to native Japanese, Korean, and English speakers. The results of these tests suggest that native Japanese speakers count the number of morae not only by the duration of vowels, but also by the accentual change which indicates the boundary between morae. On the other hand, non-native speakers count the number of morae only by the duration of vowels.
Speech recognition in a system for teaching Japanese
Authors: Najmi Amir , Bernstein Jared
Published: October 2005

Automatic speech recognition (ASR) is implemented and tested in a system to offer first-level, computer-based exercises in the Japanese language for beginning high school students. The paper describes a development project designed to identify the strengths and limitations of current ASR technology in the development of materials for computer-assisted interactive spoken language education. With current ASR technology, several kinds of pedagogically useful exercises can be constructed that should aid spoken language acquisition in a non-native student. A system design is presented, along with some example exercises and a description of methods that are used to evaluate its effectiveness with students at different levels of proficiency. At the present time, there is no agreed-upon set of ASR functions that is adequate to support many common types of teacher–student interactions. The project has begun to address such issues in the course of developing and field testing a representative set of exercises. [Work supported by the U.S. Department of Education.]