bluuebunny/crossref_metadata_2025 huggingface dataset:
A pencil‐beam photon dose algorithm for stereotactic radiosurgery using a miniature multileaf collimator
Authors: Dong Lei , Shiu Almon , Tung Samuel , Hogstrom Kenneth
Published: July 2002

A computer‐controlled miniature multileaf collimator (MMLC) with 4 mm leaf width and a maximum field size of has been designed as a tertiary beam‐shaping device for linac‐based stereotactic radiosurgery. The purpose of this study is to develop an accurate and efficient dose calculation model for use with the MMLC. A pencil‐beam based algorithm using a sum of three Gaussian kernels was developed to model the off‐axis ratio of MMLC fields. Because the kernel integration over a rectangular field can be solved in closed form, dose to any point from an arbitrary MMLC field can be calculated efficiently by summing dose contribution from a set of rectangular apertures and transmission blocks that model individual leaf openings or leaf transmissions. The model uses an effective rectangular field and equivalent square method for determination of depth dose and dose output. Results showed that the calculated percentage depth dose was within 1% and output factor was within 1.5% of measured data. The parameters of the pencil beam kernels were extracted by fitting measured off‐axis profiles for a few field sizes at a few depths. The accuracy of the calculated off‐axis ratio was tested by comparison with measured data for a number of MMLC fields. The algorithm was shown to be accurate to within 1.5% or 1 mm for off‐axis ratios. The algorithm computes at a speed of 34 600 data points per second on a DEC Alpha server model 2000/433 (Digital Equipment Corp., Maynard, MA), which is about 15 times faster than a Clarkson‐type summation method.
Enhancing maximum measurable sound reduction index using sound intensity method and strong receiving room absorption
Authors: Hongisto V. , Lindgren M. , Keränen J.
Published: July 2002

The sound intensity method is usually recommended instead of the pressure method in the presence of strong flanking transmission. Especially when small and/or heavy specimens are tested, the flanking often causes problems in laboratories practicing only the pressure method. The purpose of this study was to determine experimentally the difference between the maximum sound reduction indices obtained by the intensity method, RI,max, and by the pressure method, Rmax. In addition, the influence of adding room absorption to the receiving room was studied. The experiments were carried out in an ordinary two-room test laboratory. The exact value of RI,max was estimated by applying a fitting equation to the measured data points. The fitting equation involved the dependence of the pressure-intensity indicator on measured acoustical parameters. In an empty receiving room, the difference between RI,max and Rmax was 4–15 dB, depending on frequency. When the average reverberation time was reduced from 3.5 to 0.6 s, the values of RI,max increased by 2–10 dB compared to the results in the empty room. Thus, it is possible to measure wall structures having 9–22 dB better sound reduction index using the intensity method than with the pressure method. This facilitates the measurements of small and/or heavy specimens in the presence of flanking. Moreover, when new laboratories are designed, the intensity method is an alternative to the pressure method which presupposes expensive isolation structures between the rooms.
Auditory nerve fiber responses to electric stimulation: Modulated and unmodulated pulse trains
Authors: Litvak Leonid , Delgutte Bertrand , Eddington Donald
Published: July 2002

Many modern cochlear implants use sound processing strategies that stimulate the cochlea with modulated pulse trains. Rubinstein et al. [Hear. Res. 127, 108 (1999)] suggested that representation of the modulator in auditory nerve responses might be improved by the addition of a sustained, high-rate, desynchronizing pulse train (DPT). In addition, activity in response to the DPT may mimic the spontaneous activity (SA) in a healthy ear. The goals of this study were to compare responses of auditory nerve fibers in acutely deafened, anesthetized cats elicited by high-rate electric pulse trains delivered through an intracochlear electrode with SA, and to measure responses of these fibers to amplitude-modulated pulse trains superimposed upon a DPT. Responses to pulse trains showed variability from presentation to presentation, but differed from SA in the shape of the envelope of the interval histogram (IH) for pulse rates above 4.8 kpps (kilo pulses per second). These IHs had a prominent mode near 5 ms that was followed by a long tail. Responses to modulated biphasic pulse trains resembled responses to tones in intact ears for small (<10%) modulation depths, suggesting that acousticlike responses to sinusoidal stimuli might be obtained with a DPT. However, realistic responses were only observed over a narrow range of levels and modulation depths. Improved coding of complex stimulus waveforms may be achieved by signal processing strategies for cochlear implants that properly incorporate a DPT.
Second harmonic sound field after insertion of a biological tissue sample
Authors: Zhang Dong , Gong Xiu-fen , Zhang Bo
Published: July 2002

Second harmonic sound field after inserting a biological tissue sample is investigated by theory and experiment. The sample is inserted perpendicular to the sound axis, whose acoustical properties are different from those of surrounding medium (distilled water). By using the superposition of Gaussian beams and the KZK equation in quasilinear and parabolic approximations, the second harmonic field after insertion of the sample can be derived analytically and expressed as a linear combination of self- and cross-interaction of the Gaussian beams. Egg white, egg yolk, porcine liver, and porcine fat are used as the samples and inserted in the sound field radiated from a 2 MHz uniformly excited focusing source. Axial normalized sound pressure curves of the second harmonic wave before and after inserting the sample are measured and compared with the theoretical results calculated with 10 items of Gaussian beam functions.
Auditory normalization of French vowels synthesized by an articulatory model simulating growth from birth to adulthood
Authors: Ménard Lucie , Schwartz Jean-Luc , Boë Louis-Jean , Kandel Sonia , Vallée Nathalie
Published: July 2002

The present article aims at exploring the invariant parameters involved in the perceptual normalization of French vowels. A set of 490 stimuli, including the ten French vowels /i y u e ø o ɛ œ ɔ a/ produced by an articulatory model, simulating seven growth stages and seven fundamental frequency values, has been submitted as a perceptual identification test to 43 subjects. The results confirm the important effect of the tonality distance between F1 and f0 in perceived height. It does not seem, however, that height perception involves a binary organization determined by the 3–3.5-Bark critical distance. Regarding place of articulation, the tonotopic distance between F1 and F2 appears to be the best predictor of the perceived front–back dimension. Nevertheless, the role of the difference between F2 and F3 remains important. Roundedness is also examined and correlated to the effective second formant, involving spectral integration of higher formants within the 3.5-Bark critical distance. The results shed light on the issue of perceptual invariance, and can be interpreted as perceptual constraints imposed on speech production.
Prediction of the vibro-acoustic transmission loss of planar hose-pipe systems
Authors: Munjal M. L. , Thawani P. T.
Published: July 2002

Vibro-acoustic energy travels through hose walls as longitudinal waves and flexural waves, apart from the sound waves through the fluid medium inside. Longitudinal waves in the hose wall are coupled to the sound waves inside by means of the hose-wall Poisson’s ratio. Both in turn get coupled to bending or flexural waves because of the energy transfer or interaction at the bends. For any of these three types of waves incident on one end of a hose, waves of all the three types may be transmitted on the other end because of their dynamical coupling with one another. Therefore, in the present paper, expressions have been derived for the 3×3 transmission loss matrix for a two-dimensional or planar piping system in terms of elements of the overall 8×8 transfer matrix of the system. These expressions have then been used in a comprehensive computer program to evaluate the vibro-acoustic performance of hoses, with particular application to the automotive climate control systems with gaseous as well as liquid media. Finally, parametric studies have been made that have led to some general design guidelines.
Noise reduction by a barrier having a random edge profile
Authors: Ho Steve S. T. , Busch-Vishniac Ilene J. , Blackstock David T.
Published: July 2002

Sound generally reaches the shadow zone behind a noise barrier by diffraction, or scattering, from the edge at the top of the barrier. By redirecting the incident sound into the shadow zone, the edge acts as a line source. For the traditional straight-edge barrier, the line source is coherent. Since a crooked line source is less coherent, we propose to improve barrier performance by making the edge randomly jagged. Laboratory model experiments to compare insertion loss of straight- and jagged-edge barriers are reported here. A spark was used as a point source, the barriers were thin (compared to a wavelength), and ground and meteorological effects were not important. After preliminary measurements showed that a jagged edge can produce significantly more insertion loss at high frequency, a three level full factorial experiment was done. The results led to an empirical equation for insertion loss of a jagged-edge barrier. Improvement over the straight barrier was found to increase with jaggedness. An unexplained result was the poorer performance of the jagged-edge barrier at low frequency.
Spectral weights in level discrimination by preschool children: Analytic listening conditions
Authors: Stellmack Mark A. , Willihnganz Melodie S. , Wightman Frederic L. , Lutfi Robert A.
Published: July 2002

In this series of experiments, adult and child listeners were required to attend to a target tone in the presence of two distracters and to indicate in which of two intervals the target tone had the higher level. The attentional weight listeners placed on each component was estimated by computing the correlation between the level change of each component across intervals and the listener’s response. In the first experiment, weights were obtained as a function of the mean level of the distracters (250 and 4000 Hz) for a 1000-Hz target. No consistent differences between the weighting functions of children and adults were observed. In a second experiment, weights were obtained as a function of the harmonic relationship between the distracters (250 and 4000 Hz, or 270 and 4320 Hz) and the 1000-Hz target. No difference was observed between the weighting functions computed with harmonic and inharmonic complexes. In the final experiment, each component of the complex (250, 1000, and 4000 Hz) was identified as the target in separate blocks of trials. In general, adults were able to weight the target component appropriately regardless of its frequency, while children tended to weight all components equally. The results suggest that preschool listeners may exhibit poorer attentional selectivity than adults.
Normal mode analysis of acoustic thermometry of ocean climate receptions using short-time Fourier techniques
Authors: Wage Kathleen E. , Baggeroer Arthur B. , Preisig James C.
Published: July 2002

The effects of internal waves on the coherence of propagating modes and the validity of the adiabatic assumption are very important issues in both matched-field processing and acoustic tomography. While much theoretical research has been done on long-range propagation of modes in deep water, there have been few opportunities to compare theoretical predictions with experimental measurements. Deployment of mode-resolving vertical arrays as a part of the Acoustic Thermometry of Ocean Climate (ATOC) experiment has provided data sets, which may offer insights about mode coherence at long ranges. This study examines the modal composition of ATOC receptions using the short-time Fourier techniques described in earlier work [Wage et al., J. Acoust. Soc. Am. 101, 3113(A) (1997)]. Initial results reveal a frequency selectivity in the arrivals for the lowest ten modes. Since frequency-selective effects can be modeled by a random multipath channel, the problem of estimating channel characteristics from pulse-compressed M-sequence receptions is discussed. In particular, this study investigates various techniques of averaging across receptions to obtain the mean arrival time and spread for each mode. [Work supported by ONR.]
Nonlinear phenomena of high-amplitude vibration of a piston in a gas-filled liquid
Authors: Rudenko Oleg , Andreev Valery
Published: July 2002

Nonlinear phenomena are known to be significant after the wave of moderate amplitude passes a long distance through a weakly dissipative medium. Such ‘‘accumulative’’ effects are studied exhaustively by nonlinear wave physics. In contrast, the ‘‘local’’ nonlinearities are studied incompletely. Such nonlinear behavior can be demonstrated by a piston immersed in liquid and vibrating with high amplitude. This piston subjected to a harmonic load can radiate not only the fundamental frequency but high-order harmonics as well. Moreover, reaction to high-power radiation can create an additional nonlinear resistance to a piston motion. Local nonlinear phenomena are expessed clearly at vibration velocities comparable with the sound speed of the surrounding medium. Such a case can be realized using liquids containing gas bubbles where sound velocity is much less than one in a pure liquid. This work is devoted to the theoretical calculation of the temporal and spectral characteristics of a nonlinear wave radiated by a piston subjected to a harmonic external force. Two different problems are discussed corresponding to the piston considered as a linear and as a nonlinear vibrating system. [Work supported by RFFI and CRDF.]
Locating ridge seismicity near Ascension Island using hydroacoustic and seismic data
Authors: Hanson Jeffrey A. , Given Holly K.
Published: July 2002

Recently, there has been a surge of interest in monitoring small-scale, mid-ocean ridge seismicity as made possible by the increasing availability of data from military-run hydrophone arrays. In the past, long-term ridge seismicity has been studied using the global networks of seismic stations. Since the young lithosphere at the ridge is relatively weak, it is not able to support large earthquakes and much of the seismicity associated with active deformation is not detected by the seismic networks. In addition to seismic body waves, mid-ocean ridge earthquakes usually produce a T phase—a water-borne acoustic wave—which travels great distances with little attenuation and is well recorded by hydrophones. This paper examines earthquakes from a section of the Mid-Atlantic Ridge near Ascension Island, using data collected from five U.S. Air Force hydrophones that surround the island and the seismic station ASCN located on the island. By integrating the hydroacoustic T phase and the local body-wave phases, earthquakes can be located down to a magnitude of 2.8 on a segment of the ridge with an accuracy of about 5 km.
A multiresolution analysis of scattering by a pair of local regions of complex heterogeneity
Authors: McCoy John J. , Steinberg Ben Z.
Published: July 2002

The scattering applies to flexure waves in a beam. Each of the local regions have a spatial extent that is a small multiple, say 2 or 3, of the length of the waves in the homogeneous background beam. The complexity of the heterogeneity refers to an irregular variation on a length scale that is a small fraction, say 1/100, of the size of the scattering region. A multiresolution analysis refers to a two-step solution methodology, by which an ‘‘effective’’ property description of the scatterers is first obtained on accomplishing a formulation substructuring in a wavelet-based phase space. The spatially filtered component of the scattered field, i.e., the only component that obtains outside the regions of heterogeneity, is then obtained via a formulation expressed in this effective description. Demonstrated, both analytically and numerically, is that the interaction of the scattering regions is accommodated in the second step of the solution procedure. Thus the effective description of each of the regions is that which applies in the absence of the second region, provided the regions do not overlap.
Equivalent phased array methods to predict acoustic fields of planar and focused ultrasound transducers
Authors: Moros Eduardo G. , Fan Xiaobing , Straube William L.
Published: July 2002

Acoustic fields generated by single-source ultrasonic transducers were predicted accurately by combining phased array theory and the Rayleigh–Sommerfeld diffraction integral. Two methods were developed and experimentally tested. The first is the equivalent phased array method (EPAM), which treats any small transducer as a phased array composed of many square elements [Moros et al., J. Acoust. Soc. Am. 101, 1734–1741 (1997)]. The second method, called CREPAM for the concentric-ring equivalent phased array method, was developed for larger axisymmetric transducers. The goal of both methods is to determine the excitation source of the equivalent phased array employing an inverse technique and data measured at a plane in the near field and perpendicular to the transducer’s axis. The determined excitation source and equivalent phase array can then be used to compute the acoustic field from the measurement plane to the far field. It was demonstrated that both methods accurately predict the location of major grating lobes and general patterns of the near and far pressure fields for several planar and focused transducers. These methods should be useful in diagnostic and therapeutic ultrasound applications where transducer-specific field characteristics are important. [Supported by NCI Grant R29-CA63121.]
Coherence calculations for propagation through anisotropic, turbulent velocity fluctuations
Authors: Wilson D. Keith
Published: July 2002

Previous treatments of the mutual coherence function (MCF, describing the coherence between the signals received by two sensors as a function of their spatial separation) have been based on isotropic turbulence models. However, acoustic waves propagating through the atmosphere are strongly affected by a large-scale turbulence structure, which is anisotropic by nature. In this paper, the MCF is calculated using several rigorous, anisotropic models for turbulent velocity fluctuations in the neutral atmospheric shear layer: a generalized Gaussian model; a generalized von Kármán model; the Kristensen et al. model [Bound. Layer Meteor. 47, 149–193 (1989)]; and Mann’s rapid-distortion, shear model [J. Fluid Mech. 273, 141–168 (1994)]. Although it is possible to obtain analytical results for the MCF for the isotropic Gaussian model and von Kármán models, one can no longer do so when these models are extended in a suitable fashion to the anisotropic case. However, it is not difficult to obtain numerical results. By comparing the anisotropic models to their isotropic versions, it is shown that anisotropy can significantly affect coherence, even when the spacing of the sensors is small (in comparison to the height from the ground).
Backscattering enhancements due to retroreflection of leaky Rayleigh waves at the truncation of a finite-solid cylinder: Measurements and test of a theory
Authors: Gipson Karen , Marston Philip L.
Published: July 2002

Leaky surface waves (such as Rayleigh waves) once launched on an elastic object will undergo partial reflection at the truncations of the object. Under certain conditions, such reflections can radiate locally flat acoustic wavefronts with a reversal of the acoustic-wave vector, and thus a large backscattered signal is produced. In the present experiments, a solid stainless-steel cylinder was ensonified through an angular region, which included the conditions for launching meridional and helical Rayleigh waves, and the resulting backscattering enhancements are consistent with hypothesized reflection processes. For the enhancement associated with a meridional ray, the observed peak magnitude of the retroreflected signal is in general agreement with approximate theoretical predictions from a convolution formulation [P. L. Marston, J. Acoust. Soc. Am. 102, 358–369 (1997)]. Helical ray contributions are also observed, but these are generally weaker at ultrasonic frequencies.
Bravais effective refractive index for tilted plastic cylinders and the caustic-merging transition in the meridional plane: Demonstration of an optical analogy
Authors: Marston Philip L. , Mount Catherine M. , Thiessen David B.
Published: July 2002

Some solid scatterers in water such as plastic cylinders do not support leaky Rayleigh waves because the shear wave velocity of the solid is less than the speed of sound in water. The high-frequency scattering from such objects is generally weak. In that case the ray diagram for transmitted shear waves is analogous to the refraction of light by an object in air. For a tilted cylindrical object, the projection of rays on a base plane may be determined by ignoring the tilt by replacing the true refractive index n by the Bravais value (n2−sin2γ)1/2/cosγ where γ is the tilt. For a circular cylinder, when the Bravais value reaches 2, the rainbow caustics merge in the meridional plane defined by the incident wave vector and the cylinder’s axis [C. M. Mount and P. L. Marston, in Light and Color in the Open Air (OSA, Washington, DC, 1997), pp. 14–16]. The merged caustics greatly enhance the scattering because of the far-field focusing of a cusp point. The analysis is also relevant to light scattering by icicles and to the scattering of sound by certain liquid-filled cylinders. [Work supported by the Office of Naval Research.]
Ray/mode duality and turning point filters
Authors: Dzieciuch Matthew
Published: July 2002

In ocean acoustic tomography, the travel time of ray arrivals are used to infer the sound-speed field. In typically dispersive channels, the ray arrivals are followed by energy, which is more easily described by vertical modes. Using a vertical array, the analyst can separate the modal energy in order to construct a dispersion diagram; a measurement of mode group velocity versus frequency for each mode number. The difference between the measured and computed group velocities would then be used in a stochastic inverse for the sound-speed field. In the WKBJ approximation, the expression for mode group velocity can be written as a function of a single parameter, mode axial inclination angle instead of the two parameters, mode number, and frequency. This fact suggests that information from modes with the same inclination angle (or equivalently the same turning point depths), ought to be combined. A turning point filter can be built that does exactly this. Perhaps it is not surprising that nature constructs rays from modes with the same turning point depths also. There is some advantage in this method over standard linear beamforming. [Work supported by the Strategic Environmental Research and Development Program through ARPA.]
How does a cone mimic a doubly closed pipe?
Authors: Ayers R. Dean
Published: July 2002

An idealized conical bore that is complete to its apex has been used as the basic model for several wind instruments with tone holes, such as oboe, bassoon, saxophone, and cornetto. The useful playing frequencies for these relatively short instruments include those near the first peak in |Z|. A uniform pipe that is closed at both ends has been proposed as the basic bore shape for the brasses, including even their strongly conical representatives, such as tube and cavalry bugle [R. D. Ayers, J. Acoust. Soc. Am. 98, 81–87 (1995)]. The relationship should be considered one of mimicry, since there are major discrepancies at low frequencies, and these extend to the first (anti)resonance or higher. The nature of that relationship and the way in which it is achieved are perhaps most easily understood by examining a conical frustum, with or without a lumped-element mouthpiece, from this new perspective. Fairly simple behaviors in the time domain provide the explanation for the mimicry in the frequency domain.
Order tracking with multiple shafts and crossing orders
Authors: Vold Håvard
Published: July 2002

Transient sinusoids that cross in frequency exhibit interaction phenomena that defy conventional tracking filter techniques. The Vold–Kalman filter explicitly uses shaft speed information from multiple shafts to decouple interacting orders through a simultaneous estimation. The estimation uses energy constraints to distribute the total signal energy between the orders. The outputs of the filter are time histories of complex envelopes of the order functions, without beating interactions and with no phase bias. The estimation is also independent of slew rates, such that highly transient events may be tracked with high fidelity. By modulating the complex envelopes by suitable carrier waves, time histories of the individual orders are obtained which can be used for sound quality studies and sound synthesis. The phase information allows for the construction of operating deflection shapes as a function of shaft, order, and shaft speed. Examples will be shown for vibrations in continuous rate belt drive transmissions and sound synthesis for torque converters.
The dolphin echolocation system
Authors: Au Whitlow W. L.
Published: July 2002

The sonar of dolphins may be the most sophisticated of all sonar systems, biological or man-made, in shallow waters and for short ranges. The Atlantic bottlenose dolphin emit short-duration (50–70 μs), high-frequency (120–140 kHz), broadband (40–50 kHz) echolocation signals with peak-to-peak amplitudes up to 228 dB re: 1 μPa. The type of signals used by dolphins play a significant role in their sonar discrimination capabilities. They have been observed detecting, classifying, and retrieving prey that is buried in sandy bottom up to a depth of about 0.3 m. In addition, controlled echolocation experiments have shown that dolphins can discriminate wall thickness, material composition, shape, and size of targets. The echolocation system of dolphins will be discussed in three parts. The first part will consider the properties of the receiving system (auditory capabilities). The second part will deal with the characteristics of echolocation signals, and the third part will consider several sonar capabilities.
High-performance loudspeaker driver design for indoor/outdoor applications
Authors: Kieltyka William J.
Published: July 2002

The design and manufacture of drivers to provide the utmost in sound quality and intelligibility and to offer weatherproof qualities is the challenge. Conventional dynamic drivers with treatment can offer limited protection, but the sound reproduction suffers markedly. An approach is used whereby each part can be chosen for performance and reliability when subjected to the worst elements. Rubber compound surrounds, cast frames, metal–alloy cones, high-tech ferrofluids, elimination of centering spiders, and magnets with special plating, are all considerations for improved design. Centering spiders are one critical component where change in mechanical characteristics is bound to occur with time. Subjected to the elements of heat, cold, humidity, etc., aging is accelerated. A speaker cannot perform for any reasonable length of time under these conditions. A design can be used that does not require the spider. When it is eliminated, the voice coil guidance system (VCGS) becomes the biggest challenge. How to make the ‘‘spiderless’’ driver perform under all traditional uses in commercial or consumer sound applications becomes another problem. The proper use of ferrofluid and specially formulated surrounds assures consistent alignment and linear movement. The additional benefits: elimination of spectral contamination caused by the spider; possible improvement in production times.
The use of the personal computer to assist in the design of loudspeaker systems
Authors: Coffeen Robert C. , Caunt Gabriel
Published: July 2002

Through the use of building acoustic analysis and design computer programs, which include the construction of building models within the program, which provide for the installation of loudspeakers within the model, and which include performance data for the loudspeakers being used, the loudspeaker system designer is provided with information and assistance which may not otherwise be readily available. The design of a typical loudspeaker system will be discussed with the aid of the computer program EASE. Then, if an auralization program is available to the designer, the performance of the loudspeaker system may be auditioned with the particular acoustical characteristics of the room in which it is installed as simulated by the building model. The performance of a particular loudspeaker system will be demonstrated using the computer program EARS, with changes to room acoustical characteristics and ambient noise conditions.
An alternative formulation for predicting sound radiation from a vibrating object
Authors: Wu Sean F. , Hu Qiang
Published: July 2002

An alternative formulation is derived for predicting acoustic radiation from a vibrating object in an unbounded fluid medium. The radiated acoustic pressure is shown to be expressible as a surface integral of the particle velocity, which is determinable by using a nonintrusive laser velocimeter. This approach is in contrast with the Kirchhoff integral formulation which requires the knowledge of both the normal component of the surface velocity and the surface acoustic pressure prior to predicting of the radiated acoustic pressure. Solutions thus obtained are unique. Moreover, the efficiency of the numerical computations is high because the surface integration can be readily implemented numerically by using standard Gaussian quadratures. Such a formulation can be readily extended to acoustic scattering problems and acoustic radiation in an interior region. This alternative formulation may be desirable to analyze the acoustic and vibration responses of a lightweight, a flexible, or a structure under an adverse environment for which a nonintrusive laser measurement technique must be used. Validations of this alternative formulation are demonstrated both analytically and numerically for vibrating spheres and right circular cylinders. [Work supported by NSF.]
Phonetic variability in /s/ and /z/ segment errors: A multitalker acoustic study
Authors: Wright Richard , Frisch Stefan
Published: July 2002

Phonological speech errors are a traditional source of evidence for phonological units, such as features and segments, in both linguistic and psycholinguistic theory. Assumptions about the unitary nature of speech errors have been brought into question by research that found evidence for subfeatural errors in speech production [R. Mowrey and I. MacKay, J. Acoust. Soc. Am. 88, 1299–1312 (1990)]. This poster presents data from an ongoing acoustic study of speech errors in /s/ and /z/ productions. Previously reported findings indicate that the errors involve either single or multiple changes in periodicity, amplitude and duration of frication, and vowel rise time [S. Frisch and R. Wright, J. Acoust. Soc. Am. 101, 3178(A) (1997)]. The data are tape recordings of an error-inducing experiment using nonsense tongue twisters. Recordings of six talkers producing four different tongue twisters targeting /s/ and /z/, for examples, ‘‘sit zap zoo sip,’’ were digitized and analyzed. This study examines the phonetic variation in featural and subfeatural errors across talkers and segmental contexts. Results suggest that details of individual talker’s production strategies and the phonetic context influence the distribution of featural and subfeatural errors. [Work supported by NIH Grant No. DC00012.]
Spectral change in the vowel formant space of Long Island vowels
Authors: Huffman Marie K. , Tamberino Elyse E.
Published: July 2002

Hillenbrand et al. [J. Acoust. Soc. Am. 97, 3099–3111 (1995)] have shown that English vowels are distinguished better by discriminant analysis when a measure of spectral change is used than when a simple formant steady-state measure is used. Many English speakers on Long Island have six front vowels instead of the five treated in most discussions of American English—in addition to low front æ, there is a higher, or ‘‘tensed’’ æ (henceforth AE). With this more crowded vowel space, spectral dynamism should be equally, if not more, important to distinguishing Long Island vowels than other varieties of English such as the Michigan English described by Hillenbrand et al. Vowels were recorded in real words of the form hVd and bVd, spoken in a frame sentence. F1 and F2 values from LPC spectral analysis were analyzed via formant plots and discriminant analysis. Preliminary results for front vowels support the hypothesis: improvement in discrimination using dynamic rather than static spectral measures was largest for ε and AE, the vowels that are closest in the vowel space. Overall use of the vowel space, including comparisons with other dialects and studies will also be presented. [Work supported by NSF.]
Acoustics and psychoacoustics of desk-top sound systems
Authors: Holman Tomlinson , Kyriakakis Chris
Published: July 2002

Sound on the desk top has some similarities and some differences from reproduction over other standardized sound systems such as those employed in the production of film and television programs. This work examines areas where the application of known acoustic and psychoacoustic principles may be used to produce a system that scales the experience of large-scale sound systems optimally to the desk-top environment. Among the methods employed are multichannel reproduction, direct-field dominant reproduction over a wide frequency range, optimal equalization for the conditions encountered by such systems, and wide frequency and dynamic ranges, among others to be discussed. Research topics underway include methods for head tracking and optimal control over the sound field for one listener, with the eventual goal of eliminating surround loudspeakers and replacing them with virtual loudspeakers. The current finding is that contemporary systems are excessively sweet-spot dependent and change the timbre too much to be acceptable professionally in this application, so the direction of research is to reduce these limitations to make a practical system with just three loudspeakers (left, right, and subwoofer).
Topics of acoustic research in mine countermeasures for littoral waters
Authors: Sovik Sturle , Bergh Nilssen Ashild
Published: July 2002

The presentation will address the status of the FFI’s (NDRE) program in mine counter measure research (MCM) and the involvement of acoustic methods, equipment, and results, therein. Assessing and countering the threat of sea mines targeting surface and sub-surface vessels are strongly dependent on the signature characteristics of the vessels and the environment of the mine–ship engagement situation. Similar considerations also apply in assessing the safety of naval vessels entering or operating in a potentially mined area. Since radiated acoustic energy and the associated seismic waves are commonly used for sea-mine actuation functions, assessment of signature characterization (acoustic), the propagation characteristics of the environment, and the noise of littoral waters constitute major research and investigation tasks at FFI. The results are contributing to advances in improving the operation capabilities of the MCM force of the Royal Norwegian Navy (RNoN). The presentation will briefly outline the objectives of our research and the programs where the acoustic methods and equipment are involved. A summary of the results and current status will also be presented. Here, emphasis on the experiments of short-range measurements in support of 3-D modeling validation and modeling results will be given.
Array element localization for vertical hydrophone arrays in the Arctic ocean
Authors: Dosso Stan E. , Sotirin Barbara J. , McDonald Vincent K.
Published: July 2002

This paper describes array element localization (AEL) for two vertical line arrays (VLA’s) of hydrophones, which comprise part of the Spinnaker Array, a 3-D sensor array in the Arctic Ocean. The AEL system associated with each VLA monitors the location of three high-frequency acoustic receivers, positioned at intervals along the array cable, by measuring travel times from five seafloor transponders. The transponders are comprised of a controller unit at the base of the array and four remote units at ranges of approximately 500 m. The accuracy to which the AEL receivers can be located depends directly on the knowledge of transponder positions. Two steps were used to accurately determine the transponder positions. First, travel-time measurements were made to an independent set of acoustic sensors suspended just below the ice. Second, use was made of the AEL travel-time data themselves. Both data sets were inverted using an iterative regularized inversion that applied a priori information to overcome the nonuniqueness/instability of the inverse problem. Monte Carlo simulation of the inversion procedure indicates that the transponders and AEL receivers are localized to an accuracy of less than 1 m.
Frequency tuning in dolphins: Evoked potential study
Authors: Popov Vladimir V. , Supin Alexander Ya.
Published: July 2002

Simultaneous tone masking and notch masking in conjunction with auditory-evoked potential recording was used to measure frequency tuning in dolphins. Tuning measurements within a range of 64–128 kHz using auditory brain-stem response (ABR) in conjunction with tone masking resulted in Q(10 dB) values of 16–18. However, this paradigm was unusable to measure frequency tuning at lower frequencies because ABRs are evoked by short transient acoustic stimuli of wide frequency band. To avoid this limitation, narrow-band sinusoidally amplitude-modulated tones were used as probes, which produce evoked potentials as an envelope-following response. With this method, tuning curves were obtained within the frequency range from 11.2–110 kHz. The Q(10 dB) values of the obtained curves varied from 12–14 at 11.2 kHz to 18–20 at 64–90 kHz. The data obtained with notch-noise maskers confirmed the results of tone masking: being approximated by roex filter form, they showed Q(10 dB) values of 18–20 and ERB of 35–39. Thus no tuning overestimation due to off-frequency listening occurred in the tone-masking experiments.
Acoustic hot-spots and breaking wave noise in the surf zone
Authors: Deane Grant. B.
Published: July 2002

While the sound of breaking deep-water waves has received considerable attention since being identified as the dominant source of wind-driven noise in the open ocean five decades ago by Knudsen, there have been relatively few acoustic measurements of breaking surf. Here measurements of the acoustic signature of breaking surf in the very near shore region are presented. A two-hydrophone acoustic system was deployed approximately 100 m from the shoreline to measure the broadband coherence of single breaking waves. The horizontal directivity of the breaking wave noise can be inverted from measurements of the noise coherence. These inversions reveal the presence of acoustic ‘‘hot-spots’’ which follow the break-point of a wave as it moves along the beach. An interpretation of the acoustic hot-spots in terms of a wave’s moving break-point and bubble plume formation will be given. [Work supported by ONR as part of the Adaptive Beach Monitoring experiment.]
Feasibilities of long-range acoustic vision in the northwest Pacific with large aperture arrays
Authors: Didenkulov Igor N. , Zverev Vitaly A. , Karlik Yakov S.
Published: July 2002

The feasibilities of the usage of large aperture stationary arrays for the acoustic observation of the northwest part of the Pacific ocean existing near the Kamchatka peninsula are described. Such an array has a plane aperture filled with 2400 hydrophones and allows the monitoring of ocean noise distribution in a horizontal view sector of 120 deg within a frequency range up to 1400 Hz. Reconstruction of ocean noise sources distribution over the ranges up to about 1000 km from a shore can be made by a method of emission acoustic spectrotomography. Spatial resolution can be improved by the incorporation of several arrays for observation. Acoustic large-scale vision may be applied for the monitoring of wind distribution, in particular storms.
Source depth estimation using modal structure extracted from vertical array ambient noise data in shallow water
Authors: Hursky Paul , Hodgkiss William S. , Kuperman William A.
Published: July 2002

Modal structure is embedded in shallow water ambient noise [Kuperman and Ingenito, J. Acoust. Soc. Am. 67, 1988–1996 (1980)]. Previously, it was reported that ambient noise measurements (SWellEx-1) using a vertical array were used to extract mode shapes [Hursky, Hodgkiss, and Kuperman, J. Acoust. Soc. Am. 98, 2971(A) (1995)]. Further analysis has characterized source distributions which would support such inversions for mode shapes. Previously, it has been shown that mode shapes alone provide sufficient information to estimate source depth [E. C. Shang, J. Acoust. Soc. Am. 77, 1413–1418 (1985) and T. C. Yang, ibid. 82, 1736–1745 (1987)]. Several depth estimators based on mode shapes extracted from ambient noise were tested on towed source data (SWellEx-96). Results of processing simulated and experimental data will be presented to assess feasibility of source depth estimation without prior environmental measurements or modeling.
Progress in microfabricated ultrasonic transducers
Authors: Ladabaum Igal , Jin XueCheng , Khuri-Yakub Butrus T.
Published: July 2002

Microfabricated ultrasonic transducers (MUTs) are generating interest as a novel alternative to piezoelectric transducers in many applications. This paper introduces the latest results, both experimental and theoretical, pertaining to the transducers the authors invented. Significant experimental results include air-coupled aluminum through transmission at 2.3 MHz with a system of 110-dB dynamic range, as well as fluid immersion transmission experiments with a dynamic range of at least 100 dB. Air-coupled transmission scans of defects in Plexiglas are demonstrated. Improvements to the authors’ fabrication process are highlighted and the paper concludes with a discussion of the energy dissipation mechanisms of the transducer. The main dissipative mechanism is, of course, radiation, but the effects of structure leakage, viscous damping, and thermal flow are introduced into the authors’ model. [Work supported by the U.S. Office of Naval Research and by a fellowship from NUS.]
Challenges in designing epidemiologic studies of hearing among children exposed to noise in utero
Authors: Frazier Linda M. , Molgaard Craig
Published: July 2002

An epidemiologic study by LaLande and colleagues has found hearing loss among children of women who were occupationally exposed to industrial noise during pregnancy. Other populations of noise-exposed women should be studied to determine if these findings can be replicated and to characterize the dose–response curve. There are many challenges to overcome in order to carry out such a study. These include: (1) obtaining access to an exposed population; (2) obtaining a large enough sample size, while avoiding selection bias; (3) accurately measuring noise exposure levels during pregnancy; (4) assessing the potential impact of confounders, such as noise exposure during toddlerhood, medical causes of hearing loss not related to noise exposure, and others; (5) obtaining adequate follow up of the cohort of children, and then obtaining a high consent rate to perform audiograms to detect small but clinically important decrements in hearing thresholds; (6) maintaining audiometry quality control if subjects are geographically dispersed; (7) obtaining funding for the study; and (8) developing preventive interventions that will minimize discrimination against women who work in noisy environments. Although these challenges exist, they are not insurmountable.
Effects of water vapor on acoustical properties of glass beads and Ottawa sand
Authors: Wang Yunlong , Sabatier James , Shields F. Douglas
Published: July 2002

Shear and compressional wave velocities have been measured in glass beads and Ottawa sand as a function of the percent of the void filled with water. Air-dry glass beads and Ottawa sand were evacuated to a pressure of about 10 mTorr and then exposed to dry nitrogen and water vapor, respectively. The results show that the water vapor increased the compressional wave velocity by a factor of 2 and shear wave velocity by a factor of 3 in glass beads at the water saturation of 0.15%. For Ottawa sand, however, the change in velocities was only a few percent for the same water saturation. At present, it is proposed that vapor condenses to form a ‘‘water lens’’ at the points of grain contact. This condensation results from surface tension lowering the vapor pressure above a curved meniscus. As yet there is no satisfactory explanation of the difference in the effect of the condensed water in the beads and sand. [Work supported by the Office of Naval Research.]
Development and validation of vibroacoustic models of irregular plates
Authors: Crimaldi Douglas D. , Singh Rajendra
Published: July 2002

Irregularly shaped cover plates used in automotive gearboxes receive vibration energy generated by meshing gears, resonantly amplify and radiate sound at many frequencies. To reduce the vehicle noise levels, a metal–plastic–metal composite plate with a constrained viscoelastic layer may be utilized. Due to the complex nature of the structure, nonuniform material properties and bolted boundary conditions, it is difficult to develop vibroacoustic models. Hence, two simplified covers must be studied first: a stamped steel cover with identical geometry and nonuniform material properties and a modified flat cover which simplifies the geometry while providing uniform material properties including thickness. Each cover is studied with free and bolted boundary conditions. A new model of the bolted connection is described and implemented. Finite element and boundary element models for each cover are developed and validated based on the experimental modal analysis and sound directivity results.
The scope of individual differences in cognitive models of spoken language understanding
Authors: Auer Edward T.
Published: July 2002

A model of spoken language understanding capable of accounting for data at the level of the individual should include: (1) a functional architecture and its processes; (2) specifications of how experience and development affect the architecture and its processes; and (3) knowledge about the range of variability that can be observed for the components of the system. Within this framework, individual differences are hypothesized to arise from the interaction of experience and biologically specified abilities. These individual differences result in systematic variation of performance in experimental tasks that can be identified with specific locations in the functional architecture and/or subprocesses. Taking into account variation due to individual differences, a model also should scale across normal and impaired populations. Evidence suggestive of the utility of this approach for understanding/predicting the performance of individuals will be presented from studies of speechreading, tactile-aid use, and cochlear-implant recipients. [This work was supported by NIH Grants DC-00695 and DC-02107.]