bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic shear modulus measurements of fiber reinforced polymers using forced torsional vibrations
Authors: Reader Wayne T. , Dlubac James J. , Deigan Richard J.
Published: October 2005

A forced torsional vibration system developed by the National Bureau of Standards [E. B. Magrab, J. Res. Natl. Bur. Stand. 89, 193–207 (1984)] for the David Taylor Naval Ship Research and Development Center is used to measure the dynamic shear modulus of viscoelastic materials. The complex shear modulus G* = G′(1 + iηG) is determined by measuring the relative amplitude and phase at the ends of a harmonically torqued right circular cylinder. The shear storage modulus and loss factor are found at frequencies ranging from 50 to 1000 Hz for fixed temperatures ranging from − 40 °C to 70 °C. An algorithm based upon the Williams-Landel-Ferry method of reduced variables [J. J. Dlubac et al., J. Acoust. Soc. Am. Suppl. 1 82 (1987), preceding abstract] is applied to the isothermal data sets to generate curves of G′ and ηG versus extended frequency range for a fixed temperature. A major feature of the system is that the cylindrical specimen dimensions may range up to 10 cm in diameter and 15 cm in height. The advantage, of course, is that the effective complex moduli of inhomogeneous materials may be determined. For example, the system may be used to investigate the dynamic properties of viscoelastic polymers containing finite sized inclusions such as chopped fibers or platelet fillers. Examples will be presented of the system's use to examine the reinforcement provided by glass fibers of several lengths randomly dispersed throughout a viscoelastic polymer.
Constrained viscoelastic layer as used to dampen structures under multiple straining modes
Authors: Bonnet M. , Garnier B.
Published: October 2005

The design of viscoelastic damping mechanisms requires both a thorough knowledge of the viscoelastic properties of materials and proper dimensioning and tools capable of handling all cases. This is particularly important when dealing with aerospace structures where the weight-to-performance ratio is critical. This point is illustrated using a specific example. Here, an aluminum honeycomb/carbon skin sandwich is damped to handle explosion shock waves over a frequency bandwidth of 1 to 10 kHz at a temperature of − 20 °C. Dynamic mechanical analysis (in modulus and loss angle) on a variety of materials led to the selection of an appropriate polyurethane elastomer. The resulting sandwich structure accounts not only for bending modes (using Ruzicka's theory), but for tension compression and shear modes as well (inspired from Y.V.K. Sadasiva Rao and B. C. Nakra). This compromise is obtained through the development of specific software, which is both simpler and quicker than a finite element analysis. A good agreement between theory and experiment at room temperature is shown. The waterfall visualization technique used is particularly useful in detailing apparent mechanisms for all configurations: bending, shearing, and tension compression. These results are so encouraging that further development of this technique is justified.
Results of a very-low-frequency acoustic propagation experiment in the Cascadia Basin
Authors: Ali Hassan B. , Fisher Craig , Authement Mona , Beckleheimer Jeff
Published: October 2005

A series of very-low-frequency (VLF) measurements were conducted recently by the Naval Ocean Research and Development Activity (NORDA) in the Cascadia Basin off the Oregon coast. Using a fixed vertical array of 16 hydrophones and a distribution of ocean bottom seismometers (OBS), the responses to cw, explosive, and air gun sound sources were monitored. The partitioning of acoustic energy between the waterborne and bottom paths is examined, using the relative responses of OBS and water-column hydrophones. Comparisons between the experimental results and predictions based on standard numerical models of acoustic propagation are used to ascertain the effects on VLF propagation of bottom shear and range-dependent topography.
High-speed normal mode calculations via Milne's equation
Authors: Ryan F. J.
Published: October 2005

A major impediment to the use of normal mode methods in deep water and/or at high frequencies is the calculational time per mode. A fast, numerically stable method of mode calculation is described which is based upon Milne's numerical solution of the Schrödinger equation. The gist of Milne's method is a phase-amplitude transformation of the linear second-order ODE for the modal depth functions into a nonlinear ODE for the quantum momentum. The resulting nonlinear equation has improved numerical stability, particularly for high-order modes. In the limit of large wavenumber, the method reduces to the conventional JWKB form, but, unlike JWKB, it is valid at turning points. An accurate and efficient computational method is developed that yields second-order convergence to an eigenvalue. The technique is demonstrated for single and multiple duct sound-speed profiles and compared to conventional propagator matrix approaches for modal calculations.
Effects of phase errors on pulse synthesis
Authors: Wood David H. , Gilbert Robert P.
Published: October 2005

One way of modeling pulse propagation in the ocean is to decompose the pulse into a weighted sum of functions eiωt, summed over various values of ω. One then solves the Helmholtz equation numerically for each required value of ω. The weighted sum of these fields then gives the desired response to the pulse in question. An alternate approach solves the parabolic equation for each required value of ω, rather than the Helmholtz equation, thereby introducing phase errors. These two results can be related by an integral transform, or transmutation, that converts the approximate solution obtained from the parabolic equation into the true solution obtained from the Helmholtz equation. As a result, corrections can be made and/or errors can be estimated or bounded.
Rigorous Gaussian-beam modeling of source functions for acoustic radiation and propagation
Authors: Maciel John J. , Felsen Leopold B.
Published: October 2005

Gaussian beam functions have favorable properties for propagating acoustic wavefields through complicated ocean environments. Use of these functions in propagation algorithms requires a decomposition of the actual or induced source distribution into a superposition of Gaussian beams. In implementations of the “Gaussian beam method” so far, the decomposition is not unique because of freely assignable parameters in the beam stack. This causes difficulties with a priori predictability [Lu et al., Geophys. J. R. Astron. Soc. (1987); Niver et al., J. Acoust. Soc. Am. Suppl. 1 81, S9 (1987)]. The source representation problem can be addressed rigorously by performing the decomposition on a lattice in a discretized (configuration-spatial wavenumber) phase space. The formulation of this discretization scheme [Bastiaans, Opt. Eng. 20, 594 (1981)] is reviewed and then applied to radiation from a cosine aperture test field distribution. It is shown how successive addition of individual displaced and (or) rotated beams with narrow, wide, or “matched” waists systematically homes in on the independently calculated reference solution, although each selection strategy emphasizes different regions in the phase space. The utility of the various options is discussed, as are the implications for synthesis of aperture fields from measured farfield data.
Rough surface scattering using the parabolic wave equation
Authors: Thorsos Eric I.
Published: October 2005

The accuracy of the parabolic wave equation (PE) for calculating scattering from randomly rough, pressure-release surfaces has been examined through comparison with exact numerical results based on solving an integral equation. To facilitate comparison with exact results, the PE problem is also converted to one of solving an integral equation: the “PE integral equation.” For the cases examined to date, the PE accurately predicts low grazing angle (θg ⩽20°) forward scattering, including multiple scattering and shadowing effects. As the grazing angle increases, it is found that the main error is an angular shift arising from propagation to and from the surface, not from the surface scattering itself. Finally, a method has been devised to compute low grazing angle backscattering with the PE. This requires the sequential solution of two integral equations to account for multiple scattering in both the forward and backward directions. [Work supported by ONR.]
Sensitivity of acoustic fields to environmental uncertainties
Authors: Dozier L. B. , Freese H. , Holmes E. S. , Tappert F. D.
Published: October 2005

A PE model has been used to compare 2D cw acoustic fields p(x,z) propagating in sound-speed fields c(x,z) to a reference acoustic field pr (x,z) propagating in the reference sound-speed field cr (x,z). Samples of the range- and depth-dependent sound-speed difference fields, δc(x,z) = c(x,z) − cr (x,z), were generated from physical models of (1) instrumental errors, (2) internal waves, and (3) baroclinic waves (mesoscale). The square modulus of the normalized inner product over depth, called ρ(x), with ρ = 1 corresponding to δc = 0, was used as a measure of the distance between ρ and ρr. Results are presented as curves of ρ(x) in dB units for various frequencies, depending on the magnitude of δc. It was found that ρ(x) decreases monotonically with range, on the average, and saturates in range at a value that decreases with increasing frequency at the rate of about 3 dB/oct. The range to saturation, called the “predictability horizon,” is surprisingly short for most frequencies of interest for moderate δc.
Acoustic monitoring and plume mapping of drilling fluid discharge
Authors: Tsai John J. , Proni John R.
Published: October 2005

An approach to monitor drilling fluid discharge from an oil rig and to map its plume distribution by high-frequency acoustics was proposed. Experiments were conducted at two nearby rigs of the East Flower Garden Bank in the Gulf of Mexico, and data were used to provide vertical plume structure and two-dimensional distribution maps at fixed depth. The ability to monitor the discharged plume continuously in time and space makes the acoustic technique more convenient and cost effective than other conventional methods.
Eigenvalue methods in the solution of acoustical scattering problems from submerged objects
Authors: Norton Guy , Keiffer Richard , Werby M. F. , Green L. H.
Published: October 2005

Waterman's extended boundary condition (EBC) method has proven to be extremely successful in dealing with scattering from submerged targets. An alternate and useful computational method (which is related to Enskog's method) separately considers the Heimholtz integral equation at exterior and interior points, as does the EBC method. However, the interior problem can be shown to transform to an eigenvalue problem, which produces eigenstates that span the space of the displacement on the object surface. The eigenstates can be used directly to solve the exterior problem and yield a numerically stable and convergent solution. This new method avoids problems encountered by the EBC method. For example, in the usual EBC approach, the unknown surface terms are expanded on a known, but to some extent arbitrary, basis set, with unknown expansion coefficients. The number of expansion terms on the surface and those of the incident partial waves must match. Computationally, this requirement can often dictate there be many more incident partial waves than strictly required for convergence of the incident field. This leads to small-incidence high-order components, that, in turn, render the resulting matrix problem ill-conditioned. The method used in this study is presented with several representative numerical examples including objects of aspect ratios of 30 to 1 for kL/2 values to 120.
Shape of acoustically levitated samples in a resonant rectangular chamber
Authors: Jackson H. W. , Barmatz M. , Shipley C.
Published: October 2005

A generalization of Laplace's formula applicable to vibrating surfaces was used to develop expressions for the equilibrium shape and position of drops and bubbles in a resonant rectangular chamber. Expanding various physical quantities in terms of spherical harmonics and applying the quantum-mechanical angular-momentum gradient formula leads to tractable expressions valid for large as well as small ka. New results for volume renormalization of drops and bubbles were also derived. The analysis takes into account acoustic radiation, surface tension, gravity, and compressibility effects. Salient features of this theory applicable to acoustic levitation will be presented. Calculated shape properties will be compared to existing results of one-dimensional theories. Also, the acoustic force dependence on ka, obtained from equilibrium position calculations, will be compared to Hasegawa's results. [Work supported by NASA.]
Boltzmann-Ehrenfest adiabatic principle applied to acoustic forces in a single-mode levitator
Authors: Putterman S. , Rudnick Joseph , Barmatz M.
Published: October 2005

An application of the Boltzmann-Ehrenfest adiabatic principle yields a fundamental relationship between the acoustic potential, acting on a sample positioned in a single-mode cavity, and the shift in the resonance of an isolated mode. The theory is very general and applies to a sample and resonant cavity of arbitrary shape and dimension. In the case of a small sample in a lossless cavity, the strict proportionality between the potential and frequency shift follows from a fairly simple argument. One useful application of this relationship is the determination of positioning forces and torques on a levitated sample from frequency shift measurements. The results of experimental measurements of the equilibrium position and orientation of a levitated sample will be presented, and their consistency with theoretical predictions will be discusssed. [Work supported by NASA.]
Perturbation calculations of eigenfrequencies of cylindrical cavity with internal spherical obstacle
Authors: Mehl James B. , Hill Robert N.
Published: October 2005

The eigenfrequencies of a hard-walled acoustic resonator are found by solving the Helmholtz equation with Neumann boundary conditions. A cavity C with an internal hard obstacle B of vanishing size was considered. As the size of the obstacle shrinks to zero, the eigenfunction does not approach an eigenfunction of the empty cavity. Thus a singular perturbation theory is required. A formalism was developed and tested by calculating the eigenfrequencies of a cylinder with an internal sphere on the axis. The results are compared with theoretical values determined by a boundary-integral-equation method (A. E. Woodling, Ph.D. thesis, University of Delaware, 1986) and experimentally [M. Barmatz et al., J. Acoust. Soc. Am. 73, 725–732 (1983)]. [Work supported in part by NASA.]
Specimen translational control capabilities using an opposed radiator acoustic levitation system
Authors: Merkley Dennis R. , Rey Charles A. , Hammarlund Gregory R. , Danley Thomas J.
Published: October 2005

Recent developments on an opposed sound-source single-axis acoustic levitation system are discussed. New and improved specimen positioning control capabilities are made available by parametric variations of the electronic drive signals. Various methods are described in which a specimen can be held in one position or translated along the axis of the levitation by simple electronic control signals. A technique is also described to provide increased specimen positioning stability using a closed loop system. [Work supported by NASA.]
Enhanced acoustic levitation using horn loaded and focusing radiators
Authors: Danley Thomas J. , Rey Charles A. , Merkley Dennis R. , Hammarlund Gregory R.
Published: October 2005

An improved piezoelectric driven, focusing acoustic radiator for acoustic levitation has been designed, tested, and evaluated. This device displays a significant improvement in focusing to produce better specimen stability and energy well shaping as well as increased transducer power bandwidth and electroacoustic conversion efficiency. Corresponding effects resulting from the horn loading of this acoustic radiator are considered as well as the benefits of using the radiator in conjunction with hot wall high-temperature furnaces. In order to aid in the evaluation of these acoustic transducer improvements, a simple and useful technique for acoustic field mapping will also be discussed. [Work supported by NASA.]
Effects of target phase in narrow-band frozen noise detection data
Authors: Isabelle S. K. , Colburn H. S.
Published: October 2005

Hit and false alarm rates were estimated for detection of a 500-Hz tone target in each often samples of 1/3-oct noise centered at 500 Hz for both NoSπ and NoSo conditions. The effects of target phase (0° and 90°) on hit rate were investigated for three subjects. Results for this narrow-band case were similar to previously reported results for wideband maskers [Gilkey et al., J. Acoust. Soc. Am. 78, 1207–1219 (1985)]. Two differences were noted. First, for NoSπ conditions, the effect of signal phase was not significant for the narrow-band maskers, whereas a small effect was reported for wideband maskers. Second, no significant correlation was observed between NoSo and NoSπ results across masker waveforms for hit and false alarm rates, whereas significant correlations for both rates were reported for the wideband experiment. The lack of effect of target phase on hit rate in the narrow-band NoSπ condition is inconsistent with models based on lateral position but consistent with the EC model and with models using the sum of the squares of interaural time and intensity differences. [Work supported by NIH.]
Inverse methods in ocean bottom acoustics
Authors: Frisk George V.
Published: October 2005

A review is presented of exact and perturbative inverse methods used to determine the acoustic properties of the bottom. The discussion concentrates primarily on inversions for properties in the top few hundred meters of sediment using input data in the frequency range 25–500 Hz. The one-dimensional, horizontally stratified case is emphasized, although implications for problems of higher dimensionality are discussed. Descriptions of theoretical methods and experimental techniques as well as examples of inversions of synthetic and experimental data are presented.
Bottom interaction effects on broadband signals
Authors: Vidmar Paul J.
Published: October 2005

This paper examines recent progress toward understanding the effects of the seafloor on low-frequency broadband signals. First, the major bottom interaction processes affecting low-frequency signals are reviewed and a simplified (single layer fluid) geoacoustic profile is shown to accurately predict their effects. A ray-based approach for simulating single bounce broadband signals is then discussed. The simulator uses the simplified geoacoustic profile to include the seafloor as part of the propagation medium. Under conditions for which the simplified profile accurately represents the acoustics of the seafloor, calculated waveforms agree well with acoustic data. Next, an approach for simulating multibounce signals interacting with a layered seafloor is described and used to show that layering in the sea floor is the likely cause of some characteristics of acoustic data that are not predicted by the single layer profile. Finally, the time spreading of broadband signals in an area with about 200 m of sediment cover is examined. Acoustics data have both small-scale (< 200 ms) and large-scale (> 1 s) time spreads. Viewing the data through several frequency bands reveals that small-scale time spreads are concentrated at high frequencies (consistent with reflection for near surface layering) while large-scale time spreads are composed primarily of low frequencies (consistent with interaction with the substrate). A simple ray analysis shows that the scattering from the region near the point of specular reflection cannot be the sole cause of the large-scale time spreading.
Synthetic modeling of shear waves in shallow marine sediments
Authors: Carter J. A. , Sutton G. H. , Barstow N. , Ewing J. I.
Published: October 2005

Full-waveform synthetic seismograms are being used to aid inversion for shear velocity and attenuation measured in shallow marine sediments off the coast of southern New Jersey in May 1986. Horizontally and vertically polarized shear waves were produced by a pair of air guns, fired alternately left and right, mounted on a sled. Initial studies demonstrated that a simple shear source in a layered medium does not fully explain the observed data. Synthetic sources mimic the experimental source by combining a dipole shear, a torque, and an explosion source (in the water). This complex source is applied to different velocity/attenuation models, and results are compared to the data. The frequency band of the synthetics is 2–15 Hz, matching the predominant frequencies of the data; the phase velocity range is 0.05 to 1.0 km/s; all possible modes within these frequency and phase velocity ranges are computed. Varying thickness and velocity of a low-velocity layer both at the top and within the sediment section produce striking changes in the character of the seismograms. Normal or inverse dispersion characterize the late-arriving guided-wave portion of the synthetics. The early-arriving diving waves generally do not exhibit appreciable dispersion. [Research supported by ONR.]
The influence of the center frequency of a narrow-band short-duration impulse noise on the growth of TTS
Authors: Laroche Chantal , Hétu Raymond
Published: October 2005

The following study has contributed to the knowledge of the effect on human hearing of the spectral content of impulse noise, a parameter that has been little studied to date. In this study, signals were computer generated to obtain 1 octave band wide impulses from a (sin x)/x numerical function. The center frequency was varied so as to generate four signals centered on 1, 2, 3, and 4 kHz. In this study, ITS growth curves were obtained with a target asymptotic effect of 8–12 dB after 30–45 min of exposure at a rate of 1 pps. The required level of exposure was determined to obtain this target effect. To reach the same level of ATS, the Lp̂ of the 1-kHz signal had to be at least 5–7 dB higher than that of the 2-kHz signal. For two of four subjects, comparable levels were required for the 3- and 4-kHz signals to obtain the predetermined effect, but these were at least 5 dB below the corresponding level for the 1-kHz signal. These results demonstrate that the spectral content of impulse is a crucial factor in the prediction of the noxiousness of this type of noise. [Work supported by IRSST.]
Digital processing of aerosonic signals
Authors: Meetham W. C. , Wildauer E. , McInerny S. A.
Published: October 2005

Experimental data were obtained from tests performed in the NASA-Ames 7- × 10-ft wind tunnel. A digitizing process for flow over a blunt-edged air foil was used to compare data with an analog system. The nearfield surface-pressure signal on the wing and the farfield aerosonic signal were cross-correlated. Digital filtering was applied to the data to suppress unwanted signals. The results of near-/farfield cross correlations show, using the digitized treatment, that there is substantial ringing, a relatively narrow-band source. Analog prefiltering exhibits a shift to lower frequency, due to frequency roll-off of the RC analog filters. It is shown that the clip-correlation (needed for analog) and the digitized full correlation methods give similar results. But the absolute value of the correlation is lost in clipping. [Work supported by NASA-Ames.]
Noise source identification on an IBM typewriter using sound intensity technique
Authors: Zeng Li J. , Crocker Malcolm J.
Published: October 2005

Noise source identification was carried out on an IBM ball element electric typewriter. The selective operation method was used to survey the vibration and sound pressure of different typewriter sources. The sound power radiation of different noise sources was measured using the two-microphone sound intensity technique. The measurements showed that the impulse radiation of the ball element striking the platen is the highest noise source, and the difference between the results with and without paper is small. Several indexes that suppose to qualify the accuracy of sound power measurements using the sound intensity technique will be discussed. [Work supported by IBM, Austin, TX.]
Determination of loudness with a programmable real-time analyzer
Authors: Brechbuehl M. , Nordby Svein Arne
Published: October 2005

An efficient program for determination of loudness as specified by Zwicker [E. Paulus and E. Zwicker, “Computer programs for calculating loudness from 1/3 octave band levels or from critical band levels” (in German), Acustica 27, 253 (1972)] is made to operate on a portable real-time analyzer. The program controls the measurement and calculates the loudness as per ISO R 532B. The user may view the results graphically on the RTA's black and white monitor or in full color on an external monitor. This completely automatic system operates without the use of an external computer due to the unique internal BASIC programmability of the real-time analyzer used. The user may easily modify the program to meet his/ her own requirements incorporating EPNdB, Stevens Loudness, etc.
VOT variability in stop-consonant productions by bilingual speakers of English and Mandarin Chinese
Authors: Lauter Judith L. , Lu Fang Ling
Published: October 2005

It has been observed [e.g., L. Williams, Percept. Psychophys. 21, 289–297 (1977)] that some bilingual speakers of Spanish and English will use language-appropriate VOT values in elicited sets of English and Spanish stops. As part of an ongoing cross-language project in repeated-measures acoustic phonetics, six native speakers of Mandarin Chinese (three females and three males) were asked to produce repetitions of English and Chinese stops in a nonsense /ha-'Ca/context. For the Chinese stops, five separate series were collected, with the stressed syllable pronounced on each of five Chinese tones. Productions were digitized via pulse code modulator, stored on video tape, and VOT segments identified and measured using waveform analysis software developed in our laboratory. Measurements of mean VOTs for each talker indicate that English and Mandarin Chinese are similar in range of absolute VOT values, clear VOT distinctions between voiced/voiceless stops, and inconsistent use of VOT to distinguish place of articulation. Further, VOT variability patterns suggest that for some of these talkers, control of VOT timing may be sensitive to tonal context, and this sensitivity may be reflected in productions of English as well as Chinese stops. [Work supported by AFOSR.]
Output constraints and cross-language differences in coarticulation
Authors: Manuel Sharon Y.
Published: October 2005

Coarticulatory patterns have been shown to vary from language to language, from speaker to speaker, and from one style or rate of speaking to the next. Many of these differences might be explained by assuming (1) that phones are associated with ranges of acceptability, that is, “acoustic output constraints,” which must not be violated by coarticulation-induced variability and (2) that these output constraints vary from language to language, speaker to speaker, etc. For this notion to have any predictive value, it is necessary, in turn, to be able to predict, to some extent, just what the acoustic output constraints are, and how they might vary. It might be expected, for example, that output constraints relax in casual speaking styles. The paper is particularly concerned with output constraints that can be understood in terms of systems of phonemic contrast. Specifically, it is predicted that when the phonemes of a language are widely spread out in the acoustic space, then the acoustic output constraints on them are less stringent than if the phonemes were crowded together. Data supporting this view will be presented for vowel-to-vowel coarticulation in three Bantu languages. [Work supported by NIH to Haskins Laboratories and NIH to M. I. T.]
Support for the frame model in Turkish and in English
Authors: Boyce Suzanne E.
Published: October 2005

The look-ahead and the frame model of anticipatory coarticulation make different predictions about lip movement in a word such as /ustu/. The look-ahead model predicts that rounding from the second vowel will spread into the intervocalic consonants, producing a single movement with a long sustained phase; the frame model predicts two distinct gestures for the rounded vowels whose tails may overlap somewhat, producing two peaks with a “trough” between. In earlier work, it was shown that for nonsense words, such as /kuktluk/, English speakers produce troughs, while Turkish speakers show plateaulike patterns. Does this mean that Turkish and English speakers employ, respectively, look-ahead and frame strategies for coarticulalion? Alternatively, the frame model holds for Turkish, but Turkish rounding gestures are larger and longer, overlapping for a greater proportion of their tails. An additive model of overlap could then produce a plateaulike pattern. Speakers' movement traces from /kiktlik/ and /kuktluk/ were added and the result compared with those for /kuktluk/; a good fit for Turkish speakers was taken as evidence for the frame model. Further, the proportion of rounding during the consonant interval was different for the two languages. Both tests support the frame model. [Work supported by NIH.]
Acoustic correlates of TENSE-LAX vowels and ATR vowels
Authors: Lindau-Webb Mona
Published: October 2005

Germanic vowel systems typically include two sets of vowels, a long, tense set and a short, lax set. Formant charts of English, German, Dutch, and Swedish show that lax high and mid vowels tend to have a more centralized position than their tense counterparts. Tense and lax low vowels do not show any such systematic relationships in the different languages. In African languages with vowel harmony, the harmonizing sets are sometimes labeled tense-lax, although a more appropriate label is advanced-retracted tongue root (ATR). Formant charts of Akan, Dho-Luo, and Agwagwune (a Nigerian language) were compared to the Germanic ones. The tense-lax and + / − ATR features behave very similarly for front vowels. Back − ATR vowels, however, tend to have a lower F2 than their + ATR counterparts, making them more peripheral, not more centre] like back lax vowels. Thus tense and ATR are not the same acoustically. Although these two features do not occur contrastively in any language, they do possibly both occur in rules within a language. Agwagwune has centralized allophones in closed syllables. These are not centralized like the lax vowels in Germanic languages, but could still be described with a feature lax.
An investigation of tag intonation in English
Authors: Sproat Richard W. , Steele Shirley A.
Published: October 2005

Tags frequently occur in English text. Common examples include “‘Are you coming?’ he said,” where “he said” is an attributive tag, and “I bought a new car, Manny,” where “Manny” is a vocative tag. Because of the frequency of tags, it is important to have an adequate treatment of their intonation for more natural sounding text-to-speech synthesis. This paper examines the intonational properties of tags in American English and discusses their phonological characterization. Investigated instrumentally are the F0 patterns employed by speakers producing tags in question and statement contexts (“‘Are you hungry?’ he said” versus “‘I am hungry,’ he said”). A phonological analysis is proposed for such tags building on work by Pierrehumbert [“The phonology and phonetics of English intonation,” Ph.D. dissertation, MIT (1980)] and Beckman and Pierrehumbert [“Intonational structure in Japanese and English,” Phonology Yearbook 3, 255–309 (1986)]. Finally the incorporation of these results into the text-to-speech system under development at Bell Laboratories is discussed, and the resulting improvement in the quality of synthesis is demonstrated.
Electromagnetic basis of acoustic perception. I. Biological structures
Authors: Cohen Glenn M.
Published: October 2005

Although hearing aids can compensate for some hearing impairments, they cannot effectively compensate for impaired functions resulting from major losses of hair cells and/or nerves. Cochlear implants are limited in their effectiveness by the number of functional cochlear neurons, surgical techniques, and current technology. Electromagnetic waves, a new approach, offer the potential of bypassing the severely impaired cochlea and directly simulating the higher auditory centers, such as the auditory cortex [P. L. Stocklin and B. F. Stocklin, TIT J. Life Sci. 9, 29–51 (1979)]. This approach is based upon the fact that excitable tissues may emit electromagnetic waves during the depolarization cycle due to energy changes in the integral membrane proteins. In this paper, the auditory application of electromagnetic waves is introduced by examining the biological structures important to acoustic perception.
Franco-American differences in the discrimination of DA from GA
Authors: Santon François , Scharf Bertram
Published: October 2005

We synthesized DAs and GAs that were supposed to differ only in the third formant, between 2 and 3 kHz. Discrimination was measured in narrow-band noise maskers centered on frequencies from 1 to 3.5 kHz. The signal-to-noise ratio was set to yield nearly 100% correct responses in the least effective masker (at 3.5 kHz) and nearly 50% in the most effective masker (at 1 or 2.5 kHz). Three American listeners yielded results similar to tuning curves. Discrimination was poorest in the 2.5-kHz noise and improved rapidly at lower and higher noise frequencies. Three French listeners gave similar results, but three others gave very different results. The signal-to-noise ratios were. 11 dB lower and discrimination was poorest in the 1-kHz noise. (One American also discriminated at the lower signal-to-noise ratio when given feedback.) Analysis of the tapes revealed a low-frequency click in the DAs but not in the GAs. Americans did not use this cue (without feedback). Some French also did not, but others did. Apparently, because natural American DAs differ from French DAs, French listeners are more likely to use artifactual cues.
Acoustic-phonetic analysis of Spanish /I/
Authors: Guirao Miguelina , Rosso Enrique A.
Published: October 2005

Acoustic measurements to examine the contribution of overlapping segments—anticipatory and carryover coarticulations—to the identification of American Spanish /I/ were performed. The consonant was combined with five vowels in naturally produced CV, VC, VCV, and CCV syllables. Acoustic profiles through analysis of formant trajectories, fundamental frequency, intensity and duration of vowel, consonant, and their overlapping segments were obtained. In searching for the corresponding critical spectral features, digitalized waveforms were modified by deleting various temporal segments in the syllable. The excised sounds were used as stimuli in identifications tests. Results indicate that the duration of the syllabic nuclei varies across front, medial, and back vowels and also in pre- and post-vocalic position. Segment /I/ presented in isolation is poorly identified. Best identifications are obtained when the stimuli are integrated by the end of the overlapping portion and the beginning of the vowel. A trading off relationship effect is observed between these two segments.
Sound generation from a transonically moving laser
Authors: Chandrasekhar Rao J. , Busch-Vishniac Ilene J.
Published: October 2005

Experimental investigations of the sound generated underwater by a moving high-power laser source have shown roughly a 25-dB boost in the pressure if the source moves at Mach one. A three-pronged approach to studying this transonic amplification phenomenon has been used: an analytical examination of the effect of including first-order entropy production terms in the equation of state, a numerical investigation of the effect of source velocity on the sound generating efficiency, and an experimental test of the validity of superposition as a function of source velocity. Results show that nonlinearities and entropy production cannot explain the amplification phenomenon. Further, the acoustic efficiency is shown to be substantially lower for a transonic source than for a subsonic source. Hence, the transonic amplification phenomenon is still not explainable. [Research supported by ONR.]
Effects of oscillatory motion on crystal growth
Authors: Thompson Charles , Mehta Vineet
Published: October 2005

This work explores how thermally induced instabilities driven by the oscillatory motion of a heated fluid affect the growth of a semiconductor crystal. The mechanisms governing interaction between the interface temperature and its growth will be presented. It will be shown that the dynamic characteristic growth front can be described by a nonlinear differential equation. Preliminary results of our analysis suggest that morphological defects in bulk materials can be attributed to the accelerated growth rate that occurs in response to high unsteady temperature gradients. The theory formulated suggests methods that could be used in controlling quality of semiconductor crystals. Finally, the implications of this theory in formulating better processes for manufacturing bulk semiconductor materials will be outlined. [Work supported by Analog Devices Professorship.]
Non-native speakers can gauge degree of foreign accent in English
Authors: Flege James Emil
Published: October 2005

Previous research indicated that non-native speakers can detect foreign accent in their second language (L2), even if they themselves speak it with an accent. This study used interval scaling to help determine whether they do so by noting native-language (L1) phones in the L2, or by noting divergences from norms established for phones in the L2. English sentences spoken by Chinese and native English talkers were presented to three groups of listeners. The Chinese listeners, who spoke English with strong foreign accents, were able to distinguish Chinese from native talkers. Those experienced in English resembled native English listeners significantly more than those who were relatively inexperienced, suggesting the experienced Chinese listeners had developed tacit knowledge of how English sentences “ought” to sound. Removing pauses from the sentences did not affect foreign accent scores, suggesting that “fluency” and “foreign accent” represent different dimensions pertaining to L2 proficiency. Chinese talkers who learned English before the age of 12 years received significantly lower scores than native English talkers. Learning an L2 before 12 years—the age often associated with the end of a “critical period”—does not guarantee accent-free pronunciation. There was no difference in foreign accent scores obtained for adult Chinese learners of English who had lived in the United States for 1 and 5 years. This suggests that amount of (unaided) L2 experience may not improve L2 pronunciation, at least beyond a certain point.
Perceptual segregation of concurrent vowels
Authors: Assmann Peter F. , Summerfield Quentin
Published: October 2005

The ability to group together the acoustic components of a voice and segregate them from competing voices is an important skill in speech communication. To study the auditory processes involved, pairs of vowels were presented simultaneously to listeners with normal hearing. Identification performance improved as the fundamental-frequency difference between the members of the pair increased. Two auditory models were compared to predict this result. The composite waveform was passed through an array of bandpass filters simulating the cat's limited frequency resolution. The “place” model estimated the two fundamentals from peaks in the profile of the rms outputs of the filters. It then sampled the profile at integer multiples of each fundamental to reconstruct the spectra of the constituent vowels. The “place-time” model estimated the fundamentals from dominant periodicities in the waveforms emerging from the filters. The amount of synchronization to each fundamental was plotted as a function of filter center frequency to reconstruct the spectra. The place-time model estimated the two fundamentals more accurately than the place model, and predicted identification responses more precisely. This outcome is compatible with the idea that a temporal analysis is involved in the segregation of concurrent sounds.
Dichotic duplex perception and modularity
Authors: Mattingly Ignatius G.
Published: October 2005

Recent work suggests that dichotic duplex perception (in which the same acoustic material simultaneously yields both a phonetic and a nonphonetic percept) occurs when the source-defining or source-localizing processes are given ecologically implausible information, and provides further evidence for the modularity of speech perception. If F3 and F1-F2 of a synthetic syllable are presented dichotically, with identical F0 contours, one hears just the expected syllable at some fixed position within the head. With a somewhat higher F0 contour on F3 than on F1-F2, one hears two voices, one at each ear, both saying the syllable. But with a considerably higher F0 contour on F3, perception is duplex: one hears a buzz at the F3 ear and the syllable at the F1-F2 ear. And if, instead, the basic pattern is modified by shifting F3 abruptly to the F1-F2 ear after 80 ms or more, one hears just the syllable, now moving across the head. But if F3 is shifted sooner, perception is again duplex: one hears a chirp at the ear initially receiving F3 and the syllable at the other ear. Evidently, sufficiently extreme conditions disrupt source definition or source localization without disrupting dichotic speech perception. Speech perception appears to be independent of these other modular processes, and therefore modular itself. [Work supported by NIH Grant HD-1994.]
Synthesis and perception of paragraph-level prosody
Authors: Silverman Kim E. A.
Published: October 2005

Discourse structure systematically influences the prosody of utterances. in this study, units of prosodic structure that span multiple sentences (prosodic paragraphs) were synthesized by (i) temporarily increasing the overall pitch range at the start of a (textual) paragraph; (ii) gradually decreasing the range over a fixed time window at the end; and (iii) lengthening the pause at the boundary. Six ambiguous multiparagraph texts were constructed: In each text the overall meaning (e.g., where a speaker's turn finished) depended on the location of one particular paragraph boundary. In a series of perception experiments, listeners heard one or another version of each text spoken by a formant synthesizer, and answered forced-choice comprehension questions. Overall results showed that (i) listeners do exploit such wide-domain prosodic organization when comprehending extended passages of connected speech, (ii) the structure can be signaled by F0 alone, although (iii) the more redundantly it is encoded, the better it will be perceived. Such prosodic structure also improves the naturalness of synthetic speech. The results argue that prosody is hierarchically organized, rather than being a strictly linear sequence of intonational phrases.
Seabed characterization from normal incidence reflectivity
Authors: Holland Charles W. , Brunson Burlie A.
Published: October 2005

Surficial values of sediment compressional velocity, density, and rms interface roughness are estimated from the coherent component of normal incidence reflectivity in the frequency range 10–1000 kHz. The Kirchhoff approximation is employed for the scattering function in the inversion algorithm such that the coherent reflection coefficient is assumed to be dependent on the distribution of the bottom heights and independent of the shape of the bottom. The functional form of the reflection data suggests that the distribution of bottom heights follows a Laplacian rather than Gaussian form for a variety of sediment types. Laboratory analysis of bottom core samples provided the means for quantitative evaluation of velocity and density predictions.
A numerical treatment of the fluid/elastic interface under range-dependent environment
Authors: Shang Er-chang , Lee Ding
Published: October 2005

The actual physical problem becomes considerably difficult and complicated when a fluid medium is interfacing with an elastic medium under range-dependent environment. In this case, a set of three “continuity conditions” must hold: (1) the continuity of vertical components of displacement, (2) the continuity of vertical components of stress, and (3) the horizontal components of stress must vanish on the interface. The implicit finite difference (IFD) scheme, used to treat the fluid/fluid interface [S. T. McDaniel and D. Lee, J. Acoust. Soc. Am. 74, 855 (1982)] can be extended to treat the fluid/elastic interface with some modifications. In this presentation, a numerical procedure is proposed to treat the fluid/ elastic interface under a range-dependent environment. An attractive feature of this numerical model is that it is readily adaptable into the existing IFD code without excessive effort. Some computational problems will also be discussed.
Transmission of sound and beams through a water-sediment interface
Authors: Muir T. G. , Lunde N. L.
Published: October 2005

The computations of Schmidt and Jensen [J. Acoust. Soc. Am. Suppl. 1 76, S10 (1984)] are extended to examine the penetration of sound beams into a sand and a mud sediment as a function of frequency, grazing angle, beam size, and pulse shape. The computations are made with the SAFARI model, an exact numerical solution to the wave equation in horizontally stratified environments. The effects of sediment attenuation and rigidity are accounted for. Beam shape contours and loss coefficients in transmission through the interface are presented. The effect of interface transmission on the integrity of propagating pulse waveforms is discussed. It is shown that decreasing the frequency to the low kHz range enhances the penetration into rigid sediments at low grazing angles (below the critical grazing angle). However, this results in a geometric dispersion effect on the transmitted waveforms, which destroys the coherence of pulsed signals.
Acoustic transmission across the water/sediment interface measured during in situ experiments
Authors: Satkowiak Lawrence J.
Published: October 2005

A series of acoustic measurements were made to measure the transmission of acoustic energy across the water/sediment interface. The in situ measurements utilized a three-dimensional array of hydrophones as acoustic receivers buried in the sediment. The acoustic sources were mounted on a movable tower located on the seafloor. The transmission was measured as a function of grazing angle, frequency, and pulse shape for two distinctly different sediment types, namely, fine sand and soft mud. The experimental results presented will be compared to predictions made using a simple multilayered model that treats the bottom as a series of contiguous layers with known acoustical properties.