bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimal pattern recognition in signal-dependent noise as a possible basis for the Weber-Fechner laws
Authors: Makris Nicholas C.
Published: October 2005

The apparent logarithmic response of human auditory and visual perception to intensity stimulus exhibited in the Weber-Fechner laws is interpreted from the perspective of optimal pattern recognition in signal-dependent noise. The stochastic behavior of acoustic and optical fields received from both fluctuating sources and scatterers can often be well approximated with circular complex Gaussian random (CCGR) variables. Averaged intensity from a CCGR field has a standard deviation proportional to the mean. Therefore, intensity images derived from CCGR fields have signal-dependent noise known as speckle. Taking the logarithm of such intensity images homomorphically transforms the signal-dependent noise into additive signal-independent noise. It has recently been shown that matched filtering such images with hypothetical patterns in the logarithmic domain provides an optimal method for pattern recognition according to the independent perspectives offered by minimum variance unbiased estimation with Fisher information, optimal filtering, and information theory [N. C. Makris, Opt. Lett. (to be published 1995)]. This provides a mathematical justification for the use of logarithmic measurements to efficiently convey information for pattern recognition, and in this context may also provide a basis for the apparent logarithmic response of human auditory and visual perception to intensity stimulus.
Modeling the effects of spectral density on the masking of additive noise by vowel-like sounds
Authors: Espinoza-Varas B. , Kudumala Muralidhar R.
Published: October 2005

The masking of additive noise by vowel sounds is relevant to speech coding. Since the spectral density of vowels is relatively low, and varies inversely with fundamental frequency, it may limit the masking effectiveness of vowels. In this paper, an excitation-pattern (EP) approach (Moore and Glasberg, 1987) is used to model effects of spectral density on masking. EP predictions were obtained for masker densities ranging from 1.0 spectral component per Hz to 1.0 per 220 Hz, and target densities ranging from 1.0 component per Hz to 1.0 per 220 Hz. In all conditions, the overall power of masker and targets was 64.0 and 50.3 dB, respectively. For each combination of masker and target density, the EPs of the masker alone (EPm) and of the masker-plus-target (EPm+t) were obtained. The EP difference, EPD=(EPm+t)−(EPm), at each ERB was integrated (across all ERBs) to obtain an index of target detectability. For masker densities lower than ∼1.0 component per 100 Hz, detectability improved as masker density decreased; the effect of target density was small. Predictions are compared to detection thresholds for additive noise masked by either /i/ or /a/, with 100- or 200-Hz fundamentals. [Work supported by OCAST- HR4-064.]
Scattering from fluid-loaded junctions of plates and shells
Authors: Rebinsky Douglas A. , Norris Andrew N.
Published: October 2005

This paper will review recent results for several related problems involving plate and shell junctions in the presence of fluid loading. First, a general solution will be discussed which gives the acoustic and structural scattered response for two joined flat plates under unilateral fluid loading. By combining this with a related solution for the admittance matrix of the fluid-loaded plates, the behavior of a pair of semi-infinite plates in contact with fluid on one side and a mechanical structure on the other can be modeled. For simplicity, the internal frame is characterized by an impedance matrix. Based on these results, a perturbation solution can be developed for two joined curved shells under unilateral loading. The leading order term in the expansion is the previously solved case of two joined flat plates, and the next term gives an approximation of the diffracted longitudinal and shear wave fields originating from the junction of two shells. In each example considered, explicit formulas are obtained for the pressure transform, and corresponding explicit and relatively simple expressions are given for the various diffraction coefficients associated with the fluid/structure interaction. The general method of solution uses the Wiener-Hopf technique to solve dual integral equations for the acoustic pressure. The plates and shells are modeled by the classical theory of flexure and thin shell theory, respectively. Numerical results of the diffraction coefficients and the redistribution of energy at structural junctions will be presented. [Work supported by ONR.]
Acoustic pressure field evaluation of an annular cylindrical array for underwater pipeline inspection
Authors: Sumangala R. , Pillai P. R. Saseendran
Published: October 2005

Evaluation of the effective acoustic pressure field of a continuous wave, optimum spaced, point source, annular cylindrical array for underwater pipeline inspection is featured in this paper. A section of the array comprised of m×n elements is selectively energized to illuminate the region to be tested and a similarly grouped set of remaining array elements function as receivers. A steady half-power beamwidth and sidelobe levels were obtained for a radius of the array greater than 40λ. The portion of the energy reflected or reradiated from the contours of the pipeline and captured by the point source elements being nominally small can be neglected for all practical purposes. Effective acoustic pressure is computed as the Fourier transform of the impulse response of the array elements hmn(r,t) determined using the Green’s function approach. The total effective acoustic pressure over the contour of the pipeline is the sum of the weighted contributions from all radiating set of elements. A good focusing effect can be achieved by optimizing the number of elements and the radius of the array. [Work supported by CSIR INDIA.]
On the approximate factorization of scalar and matrix Wiener–Hopf kernels with applications in structural acoustics
Authors: Abrahams I. David
Published: October 2005

The Wiener–Hopf technique has proved to be an extremely powerful aid to solving problems in diffraction theory, and in particular for acoustic wave scattering. The key step in the procedure is the factorization of the Wiener–Hopf kernel into a product of two functions with (overlapping) semi-infinite regions of analyticity. However, for complex problems, such as those concerned with the interaction between fluids and structures, the representation of the scalar factors can have technical difficulties which make their computation both slow and delicate. Further, many important models of this type give rise to matrix kernels, for which no exact factorization technique has yet been devised. In this paper, a new procedure is presented to obtain approximate but explicit factorizations of both scalar and matrix kernels. As well as being simple to employ both analytically and numerically, the accuracy of the component factors can be increased almost indefinitely with little increase in numerical effort. Further, rigorous bounds on the error of these approximations are easy to find. The method is demonstrated by way of example, and the particular relevance of the new scheme to fluid/structure interaction problems is discussed.
Visualization of scattered waves resulting from an axial surface wave incident on a discontinuity of a fluid-loaded cylindrical shell
Authors: Means Steven L.
Published: October 2005

On fluid-loaded cylindrical shells there is a wave type that propagates in the axial direction at low frequencies and is characterized by a phase velocity slightly lower than the sound speed of the surrounding fluid. When such a wave is incident on a shell discontinuity, energy is scattered back along the cylinder’s axis and into the surrounding fluid. This phenomenon may be modeled by considering a wave propagating along a semi-infinite cylindrical boundary having a given surface impedance attached to a semi-infinite rigid cylinder. This model allows one to use the Wiener–Hopf technique to obtain analytic expressions, in integral form, for the scattered pressure in the surrounding fluid. These expressions are then used to obtain visualizations of the scattered field. Comparisons are made with analogous surface waves scattered by a discontinuity of an elastic plate on an elastic foundation.
Hybrid asymptotic-numerical method for evaluating diffraction coefficients
Authors: Barbone Paul E. , Harari Isaac
Published: October 2005

In complicated structural acoustics problems, the lack of relevant diffraction coefficients often limits the applicability of the geometrical theory of diffraction. A hybrid asymptotic/finite-element method is described that lends itself to the numerical evaluation of diffraction coefficients. It is based on the method of asymptotic patching. The farfield asymptotic expansion of the scattered field is patched to a finite-element interpolation of the field near the point of diffraction. This idea leads to the definition of an asymptotically equivalent boundary-value problem, which is defined on a small domain and therefore is efficiently discretized. The method is demonstrated with an application to diffraction by an imperfect wedge. [Work supported by ONR.]
Time and angle spreads due to scattering by bottom roughness and sediment volume inhomogeneity
Authors: Jackson Darrell R. , Williams Kevin L.
Published: October 2005

A bistatic scattering model that treats both roughness and sediment volume scattering is used to infer time and angle spreading for sedimentary seabeds. This model is embedded in a simulation code that predicts the received intensity time series taking account of single-bounce bistatic geometry as well as transmitter and receiver directivity. Roughness scattering is treated in the Kirchhoff approximation without invoking the stationary-phase approximation. Sediment volume scattering is treated in the perturbation approximation. Both roughness and volume inhomogeneity are assumed to be random processes with power-law spectra. The relative importance of roughness and sediment volume scattering as spreading mechanisms and the energy loss due to forward scattering are examined for a range of sediment types.
On spatial coherence and angular spread of sound forward scattered from the sea surface: Measurements and interpretive model
Authors: Dahl Peter H.
Published: October 2005

Measurements of the spatial coherence of high-frequency sound forward scattered from the sea surface are discussed, along with a simple interpretive model. The data originate from an experiment off the southern California coastline using the research platform FLIP. Measurements were made using omnidirectional sources suspended from a spar buoy (tethered to FLIP) and a line array mounted on FLIP’s hull, with range varying between 500 and 1000 m. The frequency was 20–40 kHz and the roughness parameter χ=2kh sin θ was ≫1 (where k is the acoustic wave number, h is the rms waveheight, and θ is the grazing angle); thus the measurements represent high-frequency, incoherent scattering in a single surface bounce channel. The coherence was measured across a line array oriented transverse to the direction of propagation, thereby giving an estimate of the horizontal coherence. Horizontal coherence to the degree of horizontal angular spreading and to the performance of beam forming arrays can be related. The simplest model with which to interpret these results is derived from the high-frequency, large-roughness limit of the Kirchhoff approximation. This model satisfactorily explains the data, and provides basis for a predictive model for horizontal coherence and angular spreading in surface forward scattering. [Work supported by ONR.]
High-resolution cross-well tomography measurements
Authors: Rapids Brian , Yamamoto Tokuo , Rogers Andrew , Kuru Murat
Published: October 2005

High-frequency/high-resolution marine cross-well tomography experiments have been conducted at several sites in the waters adjacent to South Florida. Frequencies ranged up to 15 kHz yielding nominal resolution of 10 cm for the tomographed cross sections. Experiments with several cross-sectional geometries determined by depth, range, source location, and receiver location were conducted, including orthogonal sections. These geometries allow determination of both two- and three-dimensional sediment compressional wave velocity structure. This structure may be evaluated for spectral content in both the twoa These spectra are computed for the experimental geometries and presented along side the calculated hydraulic structure. A companion paper being presented at this conference discusses the use of these wave-number spectra as input for modeling acoustic backscatter that was also measured at the cross-well tomography sites discussed here [Rogers etal., J. Acoust. Soc. Am.]. It is shown that cross-well tomography techniques employed on the ocean floor can provide excellent information for prediction of the acoustic backscattering strength. [Work supported by ONR.]
Inclusion of a prosodic module in spoken language translation systems
Authors: Eklund Robert , Lyberg Bertil
Published: October 2005

Current speech recognition systems mainly work on statistical bases and make no use of information signaled by prosody, i.e. the segment duration and fundamental frequency contour of the speech signal. In more advanced applications for speech recognition, such as speech-to-speech translation systems, it is necessary to include the linguistic information conveyed by prosody. Earlier research has shown that prosody conveys information at syntactic, semantic, and pragmatic levels. The degree of linguistic information conveyed by prosody varies between languages, from languages such as English, with a relatively low degree of prosodic disambiguation, via tone-accent languages such as Swedish, to pure-tone languages. The inclusion of a prosodic module in speech translation systems is not only vital in order to link the source language to the target language, but could also be used to enhance speech recognition proper. Besides syntactic and semantic information, properties such as dialect, sociolect, sex, and attitude, etc. is signaled by prosody. Speech-to-speech recognition systems that will not transfer this type of information will be of limited value for person-to-person communication. A tentative architecture for the inclusion of a prosodic module in a speech-to-speech translation system is presented.
Scattering function characterization of time and frequency spreading in shallow water propagation
Authors: Cable Peter G.
Published: October 2005

Under certain conditions the multipath time delay and frequency spread of signals propagating in shallow water can be described usefully with the ocean modeled as a randomly time-varying linear filter. Starting with an explicit physical model for the time-varying transfer function of a shallow water channel, an alternative system function, the delay-Doppler spread function, can be defined and its autocorrelation determined. A particularly simple form of the spread function autocorrelation, the scattering function, results when the propagation multipaths are uncorrelated and locally stationary in the wide sense. When the scattering function description is valid, signal propagation input–output relations can be expressed in terms of the medium scattering function and the input signal ambiguity function. The scattering function formulation will be reviewed and shown to be most useful for channels supporting many boundary-interacting paths (e.g., shallow water) at mid or high frequency. Using the scattering function the influence of the medium on different sonar signal types will be demonstrated and methods for measuring channel characteristics indicated. Channel characteristics determined from data obtained during ACT II on the New Jersey Shelf under downward refracting propagation conditions will be presented and discussed in terms of the scattering function description. [Work supported in part by ARPA.]
On the dependence of bottom scatter on frequency, grazing angle, and azimuth
Authors: Yamamoto Tokuo
Published: October 2005

The bottom scatter data from many different shallow and deep water sites by Jackson and Briggs (1992), Ogden and Erskine (1993), Hines and Barry (1992), and others show wide varieties of dependencies on frequency, grazing angle, and azimuth. Model predictions so far have not been satisfactory. For example, Mourad and Jackson (1993) suggested that the frequency dependence of bottom backscatter is due to the vertical velocity gradient. However, unrealistic velocity gradients were needed to predict the backscatter increasing with frequency. The high resolution crosswell tomography and cores of seafloor sediments show that the three-dimensional (3-D) spectra of velocity and density fluctuations within the sediments are anisotropic and dipping [Yamamoto, J. Acoust. Soc. Am. (to be published)]. It will be shown in this paper that the various dependencies of bottom backscatter on frequency, grazing angle, and azimuth observed in the data are results of the 3-D spectra of density and velocity fluctuations in sediments based on a volume scattering theory by Yamamoto [J. Acoust. Soc. Am. (in press)]. [Work supported by ONR.]
Frequency dependence of sound propagation in shallow water: Theory and experiments
Authors: Badiey Mohsen , Bongiovanni Kevin P. , Jaya Indra , Siegmann William L.
Published: October 2005

Experimental observations of broadband acoustic propagation in a known geological region of the Atlantic Generating Station (AGS) site [Badiey etal., J. Acoust. Soc. Am. 96, 3593–3604 (1994)] has prompted new approaches to understanding frequency-dependent behavior in shallow-water regions. First, recent acoustic observations and detailed geological borehole measurements are reviewed, along with a three-dimensional model of the geoacoustic data that have been developed using the kriging method. Parabolic equation modeling, including range-dependent sound speed and attenuation, is performed for both cw and broadband signals in this region. This is accompanied by normal mode investigations in which trapped modes in the layered media and range-dependent mode coupling are examined. A modal-based theory is presented to explain quantitatively the interference patterns observed in the experimental data (transmission loss versus frequency) in terms of waveguide parameters. It is shown how layered shallow-water waveguides act as bandpass filters in which broadband acoustic energy is selectively broken into narrow-band components, thereby providing new insights applicable to existing inverse techniques.
Scattering function characterization of underwater acoustic channels
Authors: Link Christopher J. , Culver R. Lee
Published: October 2005

Underwater acoustic channels can be modeled as linear, time-varying, random filters. If the wide-sense stationary uncorrelated spreading (WSSUS) assumption is valid then the scattering function [L. J. Ziomek, UnderwaterAcoustics: ALinearSystemsTheoryApproach (Academic, Orlando, FL, 1985)] completely defines the time and frequency characteristics of the channel. The scattering function is measured using traditional matched filter processing and the newer uncertainty product function (UPF) receiver [S. K. Mehta, SignalDesignIssuesfortheWignerDistributionFunctionandaNewTwinProcessorfortheMeasurementofTargetand/orChannelStructures (Ph.D. dissertation, University of Rochester, Rochester, NY, 1991)]. The structure and performance of the UPF receiver will be discussed. The theory behind the scattering function and experimental results from sites off Halifax, Canada, and in Puget Sound will be presented.
Sound scattering at surface waves in the ocean, revisited
Authors: Godin Oleg A.
Published: October 2005

In the absence of air bubbles, sound scattering at the ocean surface is usually considered to result from surface roughness in a steady homogeneous fluid. However, the roughness is a manifestation of surface waves and is inevitably accompanied by fluid motion in a subsurface layer. Being time and space dependent, these currents provide an additional physical mechanism of sound scattering. Although negligible in most cases because of the smallness of surface-wave frequency compared to sound frequency, scattering due to currents is shown to be significant at near-specular directions. The difference between results of the quasisteady (frozen medium) approximation and that of rigorous theory is pronounced in the latter case. A visual interpretation of the volume scattering enhancement in nearspecular directions and of failure of the quasisteady approximation to predict it is given. The effect of this additional scattering mechanism on the frequency spectrum of sound scattered at the ocean surface in deep and shallow water is analyzed. [Work supported by NRC.] a)On leave from P. P. Shirshov Oceanography Institute, Moscow, Russia.
Pulse modulation and frequency effects on long-range sonar displays of fish
Authors: Weston David E.
Published: October 2005

Early work on long-range sonar displays of fish is reviewed, for observations in the Perranporth Sea area. There is a concentration on the complications in interpretation arising from the use of a variety of pulse types and carrier frequencies. A useful technique was the interleaved transmission of different pulses or frequencies, permitting a comparison of virtually synoptic records. For linear frequency-modulation pulses there are dramatic changes in display appearance when pulse duration or pulse bandwidth are changed, which must be allowed for in the inversion giving fish distribution and behavior. There are further differences and problems with noise-modulation pulses; although these can perform well, they do often give very poor pictures. In contrast to the pulse-type effects there is a relatively small dependence of detailed appearance on carrier frequency for frequencies 1, 2, and 3 kHz; reflecting the slow dependence of fish school target strength on frequency. Of course system performance does depend on frequency as it does on the whole system engineering. In spite of the complications it is possible to find useful information on fish numbers, school numbers, movement, target depth, and behavior generally.
A theoretical and experimental basis for the measurement of fish migration using high-frequency acoustical scintillation
Authors: Farmer David M. , Trevorrow Mark , Ye Zhen
Published: October 2005

Salmon migrating up the Fraser River produce an identifiable scintillation signal as they pass through high-frequency acoustic paths directed transversely across the flow. The scintillation field due to the fish can be identified by its differential motion with respect to that due to background turbulence which moves downstream with the river flow. The potential of this technique is explored in terms of a model for forward acoustic scattering from fish and the application of spatial aperture filtering and reciprocal transmission analysis. Results of recent laboratory and field studies will be presented.
Small scale spatial structure in zooplankton from high-frequency acoustical measurements
Authors: Holliday D. V.
Published: October 2005

Volume backscattering was measured at multiple discrete depths at frequencies of 0.165 and 1.1 MHz from a mooring on the shelf-slope break at the northern edge of the San Pedro Basin near Los Angeles, CA. Attempts to understand temporal variability and vertical structure in the data from the mooring led us to make additional measurements along an onshore–offshore transect at this location at frequencies of 0.265, 1.1, 1.8, and 3.0 MHz. These measurements, when processed with an inverse algorithm to determine plankton size and abundance, revealed both an onshore–offshore trend and small scale structure in this environment. Results of sampling the same environment with a multiple opening–closing net sensor system (MOCNESS) are consistent with the acoustical measurements, but at the same time highlight the difficulty of sampling a heterogeneous spatial distribution with a net system. [Work supported by ONR, NSF, and Tracor Applied Sciences.]
Finite-element methods to analyze transducer array interaction
Authors: Morrow Richard E.
Published: October 2005

Understanding the effects of energy coupled from one transducer to an adjacent transducer in an array environment presents a challenging problem for the numerical analyst. Methods which minimize the number of equations to solve must be weighed against numerical accuracy and ease of model generation. Approaches based on finite elements, including ‘‘brute force’’ using planes of symmetry, the concept of marching frames, finite-element/boundary-element methods, and separation of the structural and acoustic solution domains for both linear and volumetric arrays are presented and evaluated. This evaluation will include a discussion on the adaptability of each method to parallel processing, especially using PVM software. Results for two array configurations of six MOD30 Class IV flextensional transducers will be presented for discussion.
Internal temporal structure of Mandarin syllables
Authors: Bell Alan , Liu Mei-Chun
Published: October 2005

The durational interactions among different combinations of onsets, nuclei, and codas in Mandarin Chinese syllables are examined, based on data from six speakers at normal and fast rates of speech. This report extends and refines preliminary results, based on four speakers at a normal tempo, that were reported earlier [A. Bell and M. Liu, J. Acoust. Soc. Am. Suppl. 1 87, S67 (1990)]. Effects of different onsets (/n t shtsh/), vowels (/a i u/), diphthongs (/ai au ou ia iau/), and nasal codas (/n sh/) were considered. Consistent effects of onsets, vowel height, complex nuclei, and nasal codas on both syllable and rhyme durations were found. These effects, however, were relatively small, of the order of 15% for rhyme durations, and from about 5% to 10% for syllables, apparently consistent with a hypothesis that Mandarin rhymes and syllables are perceptually invariant. On the other hand, the nature of segment compensations was more consistent with segment-local and universal mechanisms than with language-particular global timing units of rhyme or syllable. [Work supported by the University of Colorado Council on Research and Creative Work.]
Variation model for the radiation impedance of Class IV transducers III
Authors: Robinson Harold C.
Published: October 2005

Previously [H. C. Robinson and E. A. McLaughlin, J. Acoust. Soc. Am. 97, 3300(A) (1995)], the modal radiation impedance for a pair of Class IV transducers was calculated using variational methods. This model determines distinct self and mutual radiation impedance contributions between pairs of surface velocity modes, including the effects of element orientation, without requiring exact solutions to the equations of motion and boundary conditions. However, in order to model the total radiation impedance of the transducers, suitable methods for combining these modal impedances must be determined, which in turn requires that some estimate of the relative importance of each modal contribution be made. One method of determining the relative strengths is singular value decomposition [G. W. Benthien, Naval Ocean Systems Center Technical Report 1329, November 1989], which effectively allows one to determine the fluid-loaded resonances of the transducer and their associated eigenvectors. The relative magnitudes of these in-water modes will determine their importance in the total impedance. The results of this combination will be incorporated in a modified equivalent circuit which includes the effects of the ‘‘banana’’ mode. Calculations using this circuit will be made to existing equivalent circuit models as well as to experimental data.
Close-packed acoustic array element interaction
Authors: Blottman John B. , Decarpigny Jean-Noël
Published: October 2005

The acoustic array element interaction is an essential parameter determining transducer array behavior. It is characterized by the mutual radiation impedance. Low-frequency transducers in a volumetric array with small size constraints are subject to much larger interaction and scattering than in conventional arrays. This paper provides an overview of an investigation of the modal components of mutual radiation impedance. The invacuo eigenmodes of a single element are determined using the ATILA finite-element method. Selection of the modal expansion terms will be based on their radiation efficiencies. Modal radiation impedances are generated using the EQI boundary integral equation method. A simple multimode equivalent circuit model of the insitu projectors, including the interaction effects, is proposed. Comparison of the results to a full finite-element model of an array is presented.
Sensor–actuator interactions in the NRL–ABC platform
Authors: Corsaro Robert D. , Houston Brian
Published: October 2005

The ABC research platform consists of a large array of multifunctional transducers mounted on a backing structure. It was specifically constructed for underwater studies of sensor/actuator coupling mechanisms. The platform transducers are represented as a 15 tile array of ABC tiles, where each tile contains a large area actuator, pressure sensor, and velocity sensor, where the latter is constructed by summing and integrating the outputs of four accelerometers. Acoustic characteristics of the ABC tiles and platform were evaluated in the NRL Large Pool Facility, both in the freefield and when mounted on a backing structure. This paper presents results and analysis of inter- and intra-tile coupling mechanisms, including particularly an evaluation of the role of the backing structure.
Radiated power and radiation efficiency of a point driven panel
Authors: Ertel J. , Maidanik G. , Dickey J.
Published: October 2005

The partial radiation efficiency from a line-driven panel was previously defined and investigated by the authors [‘‘Partial radiation efficiency of line-driven panels,’’ J. Sound Vib. 144, 71–86 (1991)]. In the present paper, the counterpart to the previous work is presented. It is shown that the radiation efficiency, like the partial radiation efficiency, is dependent on the mechanical damping in the panel; and again, the efficiency increases with increase in the mechanical loss factor in the panel. Also, the dependence of the radiation efficiency on fluid loading is analogous to that of the partial radiation efficiency described in the previous work. In this paper, in addition, the radiated power as a function of frequency is investigated. It is shown that the radiated power appropriately diminishes with an increase in the mechanical damping. This result, in contrast, shows the fallibility of the conclusion that ‘‘a higher radiation efficiency implies, without further qualifications, more radiated power.’’ The results of computer experiments are cited in support of the various aspects in the paper.
Acoustic scattering from a fluid-loaded elastic plate with a distributed inhomogeneity of varying length scales
Authors: Cuschieri Joe M. , Feit David
Published: October 2005

Solutions were presented at the 128th and the 129th ASA meetings for the response and acoustic scattering from a fluid-loaded elastic plate with a distributed mass or stiffness inhomogeneity. The distributions considered for the inhomogeneity were a uniform distribution, a quadratic distribution, and a biquadratic distribution. It was shown in the previous presentations that below the critical frequency, there is a marked difference in the scattering between a mass inhomogeneity and a stiffness inhomogeneity. Furthermore, the scattering from the stiffness inhomogeneities was much less than that from the mass inhomogeneities. Above the critical frequency, both types of inhomogeneities generated similar scattering results. In this paper the influence of variations within the distribution of the inhomogeneity is considered. That is, apart from the overall distribution, the inhomogeneity has local changes. The inhomogeneity has two length scales, one associated with the overall distribution, where the same types of distributions as previously are considered, and one associated with the changes within the inhomogeneity distribution. The scattering from stiffness-type inhomogeneities increases with the introduction of this second length scale, while the scattering from the mass inhomogeneities is less influenced by the introduction of the second length scale. These results agree with those presented by Steinberg and McCoy at the 129th ASA meeting. [Work sponsored by ONR.]
Experimental measurements of vibrational energy and acoustic radiation for a 3-D truss
Authors: Bondaryk Joseph E. , Dyer Ira , Chiasson Leo , Fricke J.Robert
Published: October 2005

The MIT Structural Acoustics Group is making experimental measurements to determine the structural loss and radiation efficiency of an undamped, three-dimensional truss structure, constructed of 0.5-in. aluminum tubing connected by massive aluminum joints. The truss was excited with a shaker driven by wideband white noise out to 20 kHz. The total vibrational energy in the truss was calculated by spatially integrating the energy estimated from acceleration measurements made over the entire truss. This value and the total input power, as measured with an impedance head, allow estimation of the total loss factor for the truss as a function of frequency. Total radiated sound power was calculated by spatially integrating a set of average acoustic intensity measurements made over a grid surrounding the truss. Since the total radiated sound power is known, the total loss factor can easily be broken down into a structural loss factor and a radiation loss factor. These measurements show that the radiation loss is smaller than structural loss, but larger than radiation from an equivalent length single strut would predict. The additional radiation is accounted for by a factor due to multipath in the truss. This factor is frequency dependent and can be estimated from the data by comparing to theory. [Research supported by ARPA and ONR.]
Low-density granular fill for damping structural vibrations
Authors: Fricke J. Robert , Hayner Mark A.
Published: October 2005

Granular materials have been used for many years to damp structural vibrations. Often these treatments incorporate sand or lead shot. Both are heavy and provide some of their damping effect through mass loading. This paper discusses the damping properties of a low-density granular material, 3M glass microbubbles (tradename Scothlite). A paste was made using water and Scothlite and placed in an aluminum free-free beam. Resonant peaks of the beam were reduced by 10 dB, and in some cases more. The specific gravity of the Scothlite is about 0.1, so mass loading effects cannot account for the damping. Further, glass is not normally considered to be highly viscoelastic at room temperature. Rather, the attenuation mechanism is thought to be activated by the low bulk sound speed of the granular fill. With a low sound speed, the wavelength is short, and incipient attenuation in the fill becomes important. The mechanism is a combination of four possibilities: (1) small but finite intrinsic material attenuation, (2) frictional losses between rubbing grains, (3) nonlinear hystere viscous losses of the fluid flow between grains. [Research sponsored by ARPA/ONR.] a)E-mail: fricke@mit.edu
Applications of fractional calculus to the analysis of damped vibrations of viscoelastic oscillators
Authors: Rossikhin Yuriy A. , Shitikova Marina V.
Published: October 2005

Free damped vibrations of an oscillator, whose viscoelastic properties are described in terms of the fractional calculus Kelvin–Voight, Maxwell, standard linear solid models, and the models with a fractional operator, are determined. The problem is solved by the Laplace transform method. When passing from image to preimage, one is led to find the roots of an algebraic equation with fractional exponents. The method for solving such equations is proposed, which allows one to investigate the roots’ behavior in a wide range of single-mass system parameters. A comparison between the results obtained on the basis of the four models has been carried out. It has been shown that for all models the characteristic equations do not possess real roots, but have one pair of complex conjugates, i.e., the test single-mass systems subjected to the impulse excitation do not pass into an aperiodic regime in any of the magnitudes of the relaxation and creep times. Once more, a model with some fractional operator is constructed, which allows the oscillator to be both in the vibrating motion and in the aperiodic regime depending on the intervals over which the relaxation times for the given model vary, as well as on the order of fractional power and the ratio of relaxed to nonrelaxed modulus.
Burst spectral measures and formant frequencies can be used to accurately discriminate place of articulation
Authors: Hasegawa-Johnson Mark
Published: October 2005

Given an accurate burst location, four automatic measurements of the burst spectral shape and three semiautomatic formant onset measurements were used to correctly classify place of articulation of 90% of a corpus of 124 stops. At least 20 releases of each of the six English stops, in unconstrained prevocalic, preglide, or (for velar and labial stops only) pre-/r/ context, were chosen at random from the TIMIT corpus. Burst locations were marked by hand. The values of F2 and F3 20 ms later, and of ΔF2 between 20 and 50 ms later, were measured automatically, and 18% of the tokens were corrected by hand. Burst compactness, peak frequency, and mid- and high-frequency amplitude were measured automatically. In separate analyses of variance, all seven measures showed significant place effects (p<0.001). In three pairwise linear discriminants, the burst measures alone were able to classify place with 85% accuracy, showing that automatic measurements can reproduce the result of Blumstein and Stevens [J. Acoust. Soc. Am. 64 (1978)]. With seven measures, the error rate was only 10%. Most errors could be attributed to a strong labial burst and rapid formant transitions in /i/ or /r/ context, or coloration of an alveolar burst by back-cavity coupling. [Supported by a grant from NIDCD.]
Locus equations as phonetic descriptors of consonantal place of articulation
Authors: Sussman Harvey M. , Shore Jadine
Published: October 2005

This experiment tested whether locus equation coefficients, slope, and y intercept could serve as indices of place of articulation for obstruents sharing the same place of articulation across different manner classes. A previous study [C. A. Fowler, Percept. Psychophys. 55, 597–610 (1994)] reported that locus equations provided poor information for place because the mean slope for /d/ (0.47) was found to be statistically different than the mean slope for /z/ (0.42) across ten speakers. Locus equations from 22 speakers were derived from CV/t/ words with initial voiced oral stop /d/, voiceless aspirated stop /th/, nasal stop /n/, voice fricative /z/, and voiceless fricative /s/ preceding ten vowel contexts. Post-hoc tests revealed /d/=/z/=/n/ for slope means. Slopes for /d/ and /th/ were also equivalent when F2 onset measurement points were corrected to account for aspiration. Scatterplots of slopes × y intercepts revealed three nonoverlapping and distinct clusters of coordinates when the coronal group (/d, t, n, z, s/) was plotted versus labials and velars. A discriminant analysis using slope and y intercept successfully categorized all coronals as alveolars with 87.1% accuracy. The collective results support the contention that locus equations can serve as effective descriptors of consonant place of articulation across manner classes. [Work supported by NIH.]
Categorization of stop consonants in /sCs/ context
Authors: Kiefte Michael , Nearey Terrance M.
Published: October 2005

To study the effects of silence duration and frication frequency on the perception of stop consonants in /sCs/ context, a two-dimensional continuum of stimuli ranging through /finverted vee/, /finverted veests/, /fiverted veesps/ and /finverted veesks/ was synthesized. Silence inserted within the /s/ frication ranged from 0–120 ms in 13 steps of 10 ms, while the frication center frequency immediately surrounding the gap varied from 1500–4500 Hz in nine linearly spaced steps. Stimuli with a 0 ms gap had no change in overall amplitude near the insertion target, while stimuli in which frication frequency was held at 4500 Hz (that of /s/) had no change in spectral shape. Fifteen subjects were asked to categorize the stimuli as either fuss, fus-s, fusts, fusps or fusks. Subjects were told to respond with fus-s when a specific consonant was not perceived, even though two /s/ sounds could clearly be distinguished. Results from a logistic regression showed that both gap duration and the frication frequency immediately surrounding have a significant effect on categorizations of the three stop consonants (p<0.0005). However, the linearity constraint imposed by a standard logistic regression appears to be too strong. Two other possibilities—quadratic categorical boundaries and hierarchical decision processes—are discussed as alternatives. [Work supported by SSHRC.]
Acoustic cues for /θ/ in American English
Authors: Kibre Nicholas , Hata Kazue
Published: October 2005

Distinguishing between the voiceless fricatives /f/ and /θ/ is a difficult problem in natural and synthetic speech. In a previous experiment using natural stimuli [K. Hata etal., Proc. ICSLP 327–330 (1994)], it was found that adding vowel transitions increased identification for /f/ at least 15% in comparison with frication-only stimuli. However, with vowel transitions, the identification of /θ/ failed to show significant improvement. The purpose of the current study was to investigate, with an improved procedure, significant cues for /θ/ which we can use in our synthesizer. Six monosyllabic nonsense words (e.g., /fiyk/, /θayk/) were recorded. Segments of approximately 30-ms duration from different locations of /θ/ and its following vowel were spliced into f-initial words. Eight subjects were asked to identify each stimulus as ‘‘th,’’ ‘‘f’’ or ‘‘indistinguishable.’’ In the /iy/ context, /f/-initial stimuli spliced with fricative-vowel transitions from /θ/ were perceived as /θ/ 55% of the time, while stimuli involving other vowel contexts and other splices tended to be perceived as /f/. This implies that a cue for /θ/ resides in this transition when followed by a high, front vowel, but that the cue is rather obscure in the 0–5 kHz region when other vowels follow.
Improvements in the perception of American English vowels by Brazilian bilinguals
Authors: Szpigel Marialice , Bell-Berti Fredericka
Published: October 2005

Brazilians who are fluent in English have more difficulty perceiving American English vowels than consonants. This study examines vowel perception by eight native speakers of Brazilian Portuguese at the beginning and again at the end of their sixth year of study of American English (at the Instituto Brasil–Estados Unidos, Rio de Janeiro, Brazil). At this level, all students are able to speak English fluently, but with varying degrees of proficiency; the subjects had different levels of English proficiency at the beginning of the study. Their perceptions of American English vowels (produced by a native speaker of American English) will be compared at the beginning and end of the study, and will also be compared to the reported perception of American English vowels [G. Peterson and H. Barney, J. Acoust. Soc. Am. 39, 151–184 (1952)]. Changes in the students’ productions of seven American English vowels over the course of the year will also be examined. [Work supported by St. John’s University and by NIH Grant DC-00121 to the Haskins Laboratories.]
English /r/ and /l/ production in American and bilingual Japanese subjects
Authors: Naito Walter R.
Published: October 2005

The tongue shapes of American and bilingual Japanese subjects were evaluated when producing words that include /r/’s and /l/’s in English. An electromagnetic midsagittal articulometer (EMMA) system was utilized to observe and record the tongue shape. A total of six transducer coils was put on the tongue. Four were on the superior side of the tongue, and two were on the inferior side. The tongue shapes of the American subjects when producing /r/’s generally agreed with the earlier studies done by Delatree and Freeman [Linguistics 44, 28–68 (1968)]. On the other hand, the Japanese subjects had more uniform tongue shapes across subjects, which was thought to correlate with the Japanese /r/’s. [Work supported by NIH.]
Perception and production of the English /r/–/l/ contrast by Japanese speakers: Relationship between performance and learning in the two domains
Authors: Bradlow Ann R. , Yamada Reiko A. , Pisoni David B. , Tohkura Yoh’ichi
Published: October 2005

This study investigated the relationship between performance in perception and production, and the relationship between degrees of learning in the two domains within individual subjects. Eleven monolingual Japanese adults participated in an /r/–/l/ perceptual training program. Both perception data (minimal pair identification scores) and production data (recordings of /r/–/l/ minimal pair productions) were collected before and after perceptual training. Pre- and post-test production data were then evaluated by native speakers of American English in a minimal pair identification task. Results showed considerable individual variation in all aspects of the perception–production relationship. Subjects varied widely in pretest levels of performance in both perception and production, as well as in improvement in perception and production. In general, subjects who performed well in the perception pretest also had good productions at pretest; however, subjects who were low performers in the perception pretest varied in their production abilities at pretest. Additionally, there was considerable variation in the transfer of perceptual learning to production. Subjects with a relatively high degree of improvement in perception did not necessarily have a comparable degree of improvement in production. Possible sources of these individual differences, and implications for the perception–production link will be discussed.
Phrase-final lengthening and stress-timed shortening effects in native speakers and Japanese learners of English
Authors: Ueyama Motoko
Published: October 2005

This study analyzes the durational patterns of native Japanese speakers learning English, with a focus on the two major prosodic effects: phrase-final lengthening and stress-timed shortening. To investigate the significance of these effects, a production experiment was conducted, adapting the method of Beckman and Edwards [Papers in Laboratory Phonology I, 152–178 (1990)]. Native speakers, beginning Japanese learners, and advanced Japanese learners of English were compared. Results are as follows: (1) The phrase-final lengthening effect is large and the stress-timed shortening effect is small in the speech of the native English speakers and the advanced Japanese learners; (2) all Japanese speakers are more successful in applying phrase-final lengthening before larger prosodic boundaries than before smaller ones. Further analysis shows that the native English speakers make more durational contrast between lexically stressed and unstressed syllables (this is called localcontrast) and also differentiate the three degrees of boundary strength hierarchically (this is called hierarchicalcontrast). These two types of durational contrasts are considered to be effective benchmarks to assess the acquisition of English stress-timing by Japanese learners, due to their considerable correlation with learner proficiency levels.