bluuebunny/crossref_metadata_2025 huggingface dataset:
Glottal airflow voice source characteristics of 11-year-old singers
Authors: White Peta
Published: July 2002

The voice source of 18 girls and 10 boys from a music school was analyzed by inverse filtering the flow signal during sustained phonation of the vowel /a/ at three pitches (F0 between 220 and 330 Hz) using soft, mid, and loud voices. Subglottal pressure was measured as the oral pressure during the /p/ occlusion preceding the vowel. As compared to previous data on adult voices, the pressure values were high, and boys tended to use slightly higher pressures than girls. The influence of pitch and loudness variation was similar to that previously reported for adult voices. The ac flow amplitude was substantially smaller than previously reported for adults and was significantly higher in the boys than in the girls, while no significant sex differences were found for the children’s closed quotient and for the level difference between the two lowest spectrum partials. Contrary to findings for adults, the dc flow during the quasiclosed phase was greater in the boys. Overall, the present findings were similar to those previously reported for untrained children’s voices. Thus children’s voice source characteristics can be more conveniently derived from singer subjects with their greater skill in independent control of pitch and loudness.
Combined simulation of two-dimensional airflow and vocal-fold vibration
Authors: Alipour Fariborz , Titze Ingo
Published: July 2002

Self-sustained oscillation of the vocal folds was simulated by combining two-dimensional laryngeal airflow with multidimensional tissue movement. A finite-element model was used for the solution of viscoelastic waves in the tissue and a finite-volume method was used in the solution of Navier–Stokes equations for the airflow. A so-called ‘‘shadow method’’ simulated the glottal constriction in the flow model to avoid the complexity of grid movement. The two-dimensional flow equations were solved in an iterative manner until the given transglottal pressure was approximated. The flow solution was then used in the estimation of the aerodynamic forces on the tissue, required in the finite-element solution of tissue movement. The results indicate that inlet velocity profiles to the glottis are almost parabolic at any instant of time. The glottal velocity increases to its maximum at the glottal exit at the center of a jet, with values exceeding 40 m/s for 0.8 kPa of lung pressure. The jet velocity waveform is similar to that of an excised larynx and the pressure profiles are similar to those of steady flows in physical models. Also, the displacement of the inferior portion of the vocal folds leads the superior position in phase.
Resyllabification evidence for diphthongal off-glides as coda consonants
Authors: Gick Bryan
Published: July 2002

The phonological status of diphthongal off-glides has long been controversial, with some researchers classifying them as consonants, others as vowels, and still others as vocalic features. The present experiment used electromagnetometer and video data to measure the effect of following context on the labiovelar off-glide of the diphthong /aw/ for three speakers of different dialects of American English. Kinematics of lip and tongue movement were measured, with findings showing the magnitude of lip aperture to be significantly smaller when followed by /a/ than when followed by /ha/, resulting in a constriction intermediate in size between that of the preconsonantal final off-glide and that of the onset glide /w/. Such sensitivity to following context indicates a partial resyllabification of the final off-glide into the onset of the following syllable, a property heretofore observed only in coda consonants. These results support the view that diphthongal off-glides are best analyzed as consonants occupying syllable coda position. [Work supported by NSF and by NIH Grant Nos. HD-01994, DC-02717.]
Rate manipulation and stability of onset and coda structures
Authors: de Jong Kenneth J.
Published: July 2002

Stetson (1951) noted that singleton coda consonants, such as in the word ‘‘eat,’’ will shift to onset consonants, such as in the word ‘‘tea,’’ when the syllable is repeated at fast rates. Tuller and Kelso (1991), replicating Stetson’s effect, claim glottal phasing to be the relevant collective variable for examining syllable structures, and posit a dynamical model in which onsets represent a mode of coordination into which the articulatory system gets attracted. The present paper reports an experiment wherein syllables consisting of /i/ and labial stops are elicited in various rate-changing conditions. Speech rate is controlled with a metronome. Results partially support Tuller and Kelso’s model in that coda /p/ and /b/ show shifts in voice onset time to the stable values (expressed in absolute milliseconds) exhibited by onsets under increases in speech rate. In addition, results show hysteresis on the rate at which these shifts occur. However, the data show that coda configurations are also stable. When occlusion duration is measured, codas are stable across rates, while onsets are instable, shifting from longer values into the stable values exhibited by the codas. Thus, both onset and coda structures represent stable configurations, though of very different types.
Some factors influencing duration between syllables judged perceptually isochronous
Authors: Dilley Laura
Published: July 2002

This pilot study examines the influence of several factors on time intervals between syllables judged to be isochronous, including number of intervening segments and number of intervening syllables. Earlier work [Fant et al. (1991); Lehiste (1977)] has primarily been concerned with interstress intervals, rather than perceptual ‘‘beats,’’ though more recent work has examined beats per se [Couper–Kuhlen (1993)]. For our study, five labelers with musical backgrounds applied a system for labeling perceptual isochrony to 1 min each of spontaneous, read, and radio news style speech [Dilley, forthcoming]. For strings indicated as isochronous by three or more labelers we determined the intervals between the ‘‘rhythmic beats,’’ i.e., perceptually strong syllables which formed the perceived isochronous sequences. For simplicity, the ‘‘beat length’’ was taken to be the time between successive vowel midpoints (or syllabic sonorant segments) for these perceptually strong syllables. Preliminary results for 1.5 min of speech indicate that beat lengths range from 200 to 800 ms, and that there is considerable variability for successive beat lengths in a perceptually isochronous sequence. This variability can be reduced somewhat by adjusting for the number of intervening segments.
Acoustical evidence for the role of preaspiration in Norwegian
Authors: Moxness Bente H.
Published: July 2002

The Norwegian quantity system exhibits two main rhyme types; V[long]C[short] and V[short]C[long]. In addition, the two rhyme types may contain both voiced and voiceless consonants. Preaspiration is a scarce phenomenon in the world’s languages, but it is found in varying degrees in Norwegian dialects. A pilot study showed no preaspiration in rhymes containing voiced consonants. Acoustical evidence is presented as documentation for the presence of preaspiration in the production of Norwegian rhymes containing voiceless consonants. Through looking at preaspiration as a relative value of overall rhyme duration, it is shown that preaspiration is significantly greater in V[short]C[long,voiceless] rhymes compared to V[long]C[short,voiceless] rhymes. Thus preaspiration may be considered a cue to V[short]C[long,voiceless] rhymes in Norwegian. A gender difference was noted as female speakers exhibited more preaspiration than male speakers in V[short]C[long,voiceless] rhymes, perhaps due to breathier voice qualities among females. It is assumed that preaspiration in Norwegian has diminished through the development from Old Norse into modern Norwegian, and a perception study shows that preaspiration holds no perceptual value in today’s spoken Norwegian. The Norwegian quantity system is compared to the Icelandic quantity system, which resembles Old Norse. The Norwegian dialect used in the study is the Tro/nder dialect.
Small-scale matched filter array processing for spatially selective sound capture
Authors: Renomeron Richard J. , Rabinkin Daniel V. , French Joseph C. , Flanagan James L.
Published: July 2002

Matched filter array (MFA) processing has a distinct advantage over delay-sum beamforming for reverberant enclosures in that it is able to cohere significant reflected images in addition to the direct arrivals and is capable of spatial selectivity in three dimensions. However, previous study of this technique utilized a very large number of sensors, which is beyond the A/D capacity and computational power of current commercially available DSP hardware. In this paper, the results of using matched filtering with only eight sensors in real rooms are presented. It is found that a moderate amount of reverberation can be removed, which suggests that the technique may prove useful for high-quality speech pickup for teleconferencing in a small-room environment.
An efficient method achieving high-precision digital time-shifting
Authors: Liu Chen
Published: July 2002

Time shifting is an important procedure required in acoustic applications and research such as producing interaural time difference in auralization for audio virtual reality and simulating multiple inputs for spatial sound signals in research on microphone arrays. Traditional analog time-shifting methods necessitated electronic delay lines, which were a burden on hardware. Instead, more recent digital methods performed time shifting using software. However, the digital methods required an extraordinarily high-sampling rate in order to achieve a reasonable precision in time shifting. Most of the digital methods so far employed interpolation to cope with this problem, although interpolation incurred a great amount of extra computation. A high-precision frequency-domain time-shifting method was recently developed for the purpose of digital implementation of broadband beamformers [Liu and Sideman, J. Acoust. Soc. Am. 98, 241–247 (1995)]. In this study, the above method was extended to more general application contexts. The interpolation was employed implicitly in this method. The computation was required only for doing FFT and unrelated with interpolation. Theoretically, the time-shifting precision can be arbitrarily high whereas the amount of computation was kept constant. Moreover, this method can easily be implemented in real time by means of the conventional short-term Fourier transform.
Measuring the locations of penetrating acoustic ray paths into marine sediments
Authors: Boyle Frank A. , Chotiros Nicholas P.
Published: July 2002

Recent experiments at sea and in the laboratory indicate anomalously high levels of acoustic penetration into sandy marine sediments at subcritical grazing angles, which are not accounted for via current viscoelastic acoustic models for sediments. Current research is directed toward a possible physical explanation. One possibility [Chotiros, J. Acoust. Soc. Am. 97(1), 199–214 (1995)] is that the sediment acts as a Biot poroelastic medium, supporting Biot slow waves with sufficient amplitude to account for the observed penetration. Another [Thorsos et al., SACLANT Conf. Proc. CP-45, 563–569 (1997)] is that seabed interface roughness scatters a significant amount of sound into the sediment. These two mechanisms differ in their ray geometries for penetrating sound. In order to determine the relative importance of the two mechanisms, a tank experiment was performed to determine acoustic ray paths into a sandy bottom. It involved a narrow beam acoustic source directed at hydrophones in the sediment column. Initial results appear to be consistent with Biot slow-wave penetration. A description of the experimental work will be included, along with a discussion of preliminary results.
A class of low-frequency modes in range-independent fluid–solid media
Authors: Ivansson Sven
Published: July 2002

A unified treatment is given of the class of low-frequency P–SV modes whose complex phase velocities do not approach zero as fast as the frequency when the frequency is decreased toward zero. Utilizing the analyticity of the dispersion function, a complete characterization is given of these modes and the linearly viscoelastic fluid–solid media in which they occur. The two Lamb plate modes and the classical interface waves (Rayleigh, Scholte, Stoneley) all appear in a general setting, and asymptotic low-frequency expressions are given for modal slownesses and mode forms. The corresponding phase velocities will either tend to a nonzero constant or approach zero like the square root of frequency. In addition, slow modes appear whose phase velocities approach zero like three other powers of frequency: 1/3, 3/5, and 2/3. Concerning 1/3, a correction is made to a paper by Ferrazzini and Aki; 3/5 and 2/3 appear for certain bending-type waves that are slower than the classical bending wave. A less known type of interface wave also emerges from the analysis, and precise conditions for existence and uniqueness are obtained. The results are extended to interface conditions with slip. In an extreme case, yet another kind of interface wave is obtained.
Shallow-water bottom measurement with an L-shaped array
Authors: Lee Yung P.
Published: July 2002

Bottom loss was measured at a shallow-water (188 m) site off the Gulf of Mexico using an L-shaped array. The L-shaped array consisted of a vertical component 153 m long covering most of the water column and a horizontal component 240 m long laid on the bottom. A source transmitting 10-s LFMs (40–440 Hz) continuously was towed toward, then away from the array. It was towed perpendicularly to the horizontal component of the array with a CPA (closest-point approach) about 250 m away from the center of the array. With the vertical component of the array, direct, surface reflected, bottom reflected, surface–bottom, bottom–surface, and surface–bottom–surface paths were identified. Bottom loss from single bottom bounce arrival over grazing angle from 10–40 deg were measured directly using the vertical component of the array. Because the horizontal component of the array was laid on the bottom, the ‘‘(1+R) effect,’’ the coherent sum of the arrival incident on the bottom and the resultant bottom reflection for that arrival, was measured. The (1+R) measurement was used to examine the geoacoustic bottom model of the site. [Work supported by the U.S. Navy.]
High-frequency bubble scattering theory and array processing
Authors: Carey William M. , Roy Ronald A.
Published: July 2002

Microbubbles near the surface of the sea and in the water column can be an important factor limiting acoustic images in shallow water and near the surf zone. Classical theories exist which describe the scattering of sound from individual bubbles and sparse distributions of bubbles provided the damping factors are known. Backscatter and forward-scatter coherence loss can be described for random bubble distributions which are both uniform and stationary in space and time, and this results in phase correlation functions, distances, and variances. The spatial bubble population can be described by the statistical distribution of the turbulent field. This paper briefly outlines the relevant theory and applies it to free field bubble distributions at high frequencies. The impact on array processing is considered for a representative bubble size and spatial distributions. The expectation of the mean-squared array response is shown to depend on a coherence function and a coherence length proportional to the ratio of the phase correlation distance and variance which is related to the bubble spatial distribution. Extrapolations to what could be expected to be a limiting array resolution are presented for high-frequency side looking and synthetic aperture sonars. [Work supported by ONR.]
A high-order boundary-integral method for acoustic scattering by 3-D bodies in a layered fluid–solid medium
Authors: Karasalo Ilkka , Mattsson Johan
Published: July 2002

A boundary-integral equation (BIE) method is described for computing the acoustic field scattered by a 3-D object with a smooth, optionally penetrable, boundary in a layered fluid–solid medium. The medium is assumed to be horizontally homogeneous, with the extreme layers consisting of homogeneous rigid or penetrable half-spaces. The incident field is excited by a monofrequent point or line source, and the Green’s function of the layered medium is computed by an adaptive transform integral technique. The BIE is solved by a point-collocation technique using high-order B splines (BSP) and high-order numerical integration. The discretized equations are solved by an iterative method, enhanced by preconditioning with the LU factors of a related linear system for spline interpolation or spline smoothing on the scatterer surface. Numerical examples are given at frequencies of a few kHz, representative, e.g., for a seabed-penetrating parametric transducer. A benchmark example is included, in which the field from a scatterer with super-ellipsoidal shape in a homogeneous medium is computed with the BSP method, with a standard BEM technique with quadratic elements, and with the null-field (NFL) method. The BSP method is shown to be highly efficient with performance gains growing as frequency increases and/or accuracy requirements are tightened.
Inexpensive passive acoustic animal tracking system
Authors: Hayes Sean A. , Costa Daniel P. , Croll Donald , Mellinger David K. , Borsani J. Fabrizio
Published: July 2002

Marine bioacoustic research is challenged by economic, logistical, and technical barriers. A multibuoy recording system has been designed. Each buoy contains a DAT recorder (SONY D-8; 9 Hz–22 kHz) with a hydrophone (Hi-Tech HTI-SSQ-41B; 10 Hz–30 kHz) connected to one channel for collecting passive acoustic data. The second channel records time-synchronizing VHF radio signals, for computing time-of-arrival differences between buoys. A GPS data logger documents buoy position. This package is encased in a PVC spar-buoy housing. During analysis, cross correlation and peak picking time synchronize the separate recordings. Cross-correlation or waveform measurement is used to determine time-of-arrival differences of vocalizations between buoys. A hyperbolic least-squares fixing algorithm is used to calculate locations of vocalizing animals. In a calibration test, three buoys were deployed in triangle formation (1.8-km spacing). Light bulb implosions were localized with an accuracy of 0.20 km. The buoys are far less expensive (approximately $1900 each) than systems requiring towed arrays, multichannel signal conditioning/recording, and large tow ships, or fixed bottom-mounted arrays. Buoys are deployable wherever animals are located, in sea state conditions through Beaufort 5. These buoys have recorded eight marine mammal species. [Work supported by ONR, ATOC, AMNH, Friends of LML, and Myers trust fund.]
A feasibility field study of monitoring blue whales using the Pt. Sur Ocean Acoustic Observatory
Authors: Chiu Ching-Sang , Collins Curtis A. , Hager Carl A. , Miller Christopher W. , Moore Therese C. , Rocheleau Michael R. , Lashkari Khosrow , Hayes Sean
Published: July 2002

In the summer of 1997, two three-day experiments were conducted to test the feasibility of acoustically detecting, classifying, localizing, and tracking blue whales at long ranges using a former SOSUS listening array located at the Naval Postgraduate School Ocean Acoustic Observatory (OAO) at Pt. Sur, California. During each experiment, full-array data were archived continuously at the OAO. In concert with the shore-based acoustic monitoring, an aircraft was assigned to locate blue whales in the Monterey Bay National Marine Sanctuary and to direct a research vessel to a whale site. The research vessel was manned with observers and instrumented with a towed hydrophone array to ground-truth the locations of the blue whales and classify the vocalized near-field signals. These shipboard measurements were required to provide a means to separate the source signal characteristics from the multipath signatures for the calibration and validation of broadband, model-based localization methods. In this presentation, an overview of this feasibility field study is provided. Initial experimental as well as modeling results are presented, which include assessments of the predictability (i.e., variability) of the vocalized sound and the uniqueness of the location-dependent multipath structure, both are fundamental to the applicability of model-based algorithms. [Research supported by ONR.]
Incoherent localization of targets for a three-dimensional multibeam sonar imaging system
Authors: Jaffe Jules S.
Published: July 2002

One advantage that three-dimensional multibeam imaging systems have over more conventional systems is that they have the potential to track many targets that are concurrently in their field of view. As such, the accurate estimation of both position and target strength are important data which can be derived from the echo responses of an active multibeam imaging system. An algorithm has recently been developed which can be used to obtain higher positional estimates for targets than available from the preformed beams of a given multibeam system (Fish TV). The method refines a least-squares residual of the amplitudes of a set of predicted data versus a set of observed data by adjusting the parameters of a model. The parameters are the position and target strength of the target. The least-squares norm results in a maximum likelihood estimator for position and target strength in high signal-to-noise. Two fortunate aspects of the algorithm are that it takes into account the geometry of the sonar system and also uses only the amplitude data. The special collection geometry and acquisition method make these features important.
Modeling high-frequency reverberation data from coastal waters
Authors: Chin-Bing Stanley A. , Stanic Steve , Murphy Joseph E.
Published: July 2002

High-frequency (40–180 kHz) acoustic reverberation data have been taken from a region 26 miles south of Panama City, Florida. The data sets were obtained from a series of bottom scattering measurements taken in an area where the bottom was covered with coarse sand and shell fragments. Two different high-frequency scattering models designed for high-frequency reverberation predictions had previously failed to match the data. These data have been reexamined using highly accurate ocean acoustic computer models based on the finite-element solution to the Helmholtz wave equation. While these models were designed for lower frequency predictions, the availability of supercomputers allowed us to apply these models at these high frequencies. In this study, new comparisons are given to the data and to the previous modeling predictions. [Work supported by ONR/NRL and a High Performance Computing DoD grant.]
Coherent reflection loss from a Pierson–Moskowitz sea surface using the NLSSA
Authors: Broschat Shira L.
Published: July 2002

Numerical results for the incoherent bistatic scattering strength for the nonlocal small-slope approximation (NLSSA) for scattering from rough surfaces [A. G. Voronovich, Waves Random Media 6, 151–167 (1996)], using a Gaussian spectrum, were recently reported [S. L. Broschat and E. I. Thorsos, J. Acoust. Soc. Am. 100, 2702 (1996)]. The cases considered agreed well with exact integral equation results and demonstrated the potential of the NLSSA for accurate modeling of rough surface scattering. In this paper, results for the coherent reflection loss for one-dimensional surfaces are presented. Coherent loss is of particular importance in long-range acoustic propagation when the cumulative effect of multiple interactions with the surface can be significant. The lowest-order NLSSA reflection coefficient is derived, and numerical results are shown for the reflection loss at low grazing angles, using a Pierson–Moskowitz sea surface spectrum. The numerical results are compared with those of other approximate methods and agree well with exact integral equation results. [Work supported by ONR.]
Sequential interactions in the discrimination of frequency increments co-occurring with irrelevant increments in frequency, duration, or level
Authors: Espinoza-Varas Blas , Jang Hyunsook
Published: July 2002

Discrimination of target frequency increments co-occurring with irrelevant increments in frequency, duration, or level was studied. Pairs (t1,t2) of 1500-Hz, 80-ms pure tones separated by 20–120 ms of silence (ITI) were presented in a three-interval, two-alternative, forced-choice (3I/2AFC) task. On each trial, a ‘‘standard’’ pair of tones (interval 1) was followed by two ‘‘comparison’’ pairs (intervals 2 and 3), with 500 ms of silence between observation intervals. One (randomly chosen) comparison pair contained a target increment in the frequency of either t1 or t2; the size of the target increment was controlled by adaptive rules. In addition to the target increment, both comparison stimuli contained identical irrelevant increments in either the duration, frequency, or level of either t1 or t2; there was no correlation between the observation intervals containing target and irrelevant increments. Listeners had to determine which observation interval contained the target increment. Discrimination of t1 frequency was degraded by irrelevant increments in t2 frequency or t2 level, particularly at the shortest ITI of 20 ms; prolonged discrimination training lessened the effects. Discrimination of t2 frequency was not affected by irrelevant increments. [Work funded by OCAST Project HR4-064.]
Performance bounds for acoustic direction-of-arrival arrays operating in atmospheric turbulence
Authors: Wilson D. Keith
Published: July 2002

A method is described for assessing the precision of wavefront direction-of-arrival (DOA) estimates made by acoustic arrays. Arrays operating in turbulent atmospheric boundary layers are considered. The method involves calculating the Cramer–Rao lower bound, which describes the best obtainable DOA precision (performance) for a given array and environment. For simplicity, it is assumed that the source is monochromatic, and multipath effects are not considered. The predicted performance bounds are found to degrade with increasing propagation distance, increasing frequency, and increasing turbulence strength. Performance predictions using several different three-dimensional turbulence models are compared: isotropic and anisotropic Gaussian models, the von Kármán model, and the Kolmogorov model, with the last in both intermittent and nonintermittent forms. When array performance is limited by turbulence (as opposed to background noise), the turbulence model strongly affects the calculated performance bounds. The results also suggest that degradation in DOA estimates results primarily from shear-generated, small-scale fluctuations in the wind velocity. Large, boundary-layer-scale eddies may still play a significant indirect role by driving intermittent episodes of high wind shear.
Active control of sound radiation from a plate using a polyvinylidene fluoride volume displacement sensor
Authors: Charette F. , Berry A. , Guigou C.
Published: July 2002

This paper presents a new volume displacement sensor (made of shaped strips of PVDF film) and the experimental implementation of this sensor in an active control system. A design strategy for a PVDF sensor detecting the volume displacement induced by a vibrating 2D structure is presented. It is based on the modal representation of the plate response. It actually consists in designing a PVDF sensor, composed of several shaped PVDF strips bonded to the surface of the structure, in such a way that the output signal of the sensor is directly proportional to the volume displacement. The design methodology is based on the experimental measurements of the plate mode shapes (eigenfunctions) and is valid for any type of boundary conditions. The experimental implementation of such a volumetric sensor in an active control system is then presented. The experimental results obtained validates this new type of volume displacement sensor.
Selection and combination of acoustic features for the description of pathologic voices
Authors: Michaelis Dirk , Fröhlich Matthias , Strube Hans Werner
Published: July 2002

The glottal to noise excitation ratio (GNE) is an acoustic measure designed to assess the amount of noise in a pulse train generated by the oscillation of the vocal folds. So far its properties have only been studied for synthesized signals, where it was found to be independent of variations of fundamental frequency (jitter) and amplitude (shimmer). On the other hand, other features designed for the same purpose like NNE (normalized noise energy) or CHNR (cepstrum based harmonics-to-noise ratio) did not show this independence. This advantage of the GNE over NNE and CHNR, as well as its general applicability in voice quality assessment, is now tested for real speech using a large group of pathologic voices (n=447). A set of four acoustic features is extracted from a total of 22 mostly well-known acoustic voice quality measures by correlation analysis, mutual information analysis, and principal components analysis. Three of these measures are chosen to assess primarily different aspects of signal aperiodicity, while the fourth one indicates the noise content of the signal. All analysis methods lead to the same feature set that consists of a measure of period correlation, jitter, shimmer, and GNE. The two-dimensional projection of this set named “hoarseness diagram” allows a graphical illustration of voice quality that can be easily interpreted.
Model equations for nonlinear surface waves
Authors: Hamilton M. F. , Il’inskii Yu. A. , Zabolotskaya E. A.
Published: July 2002

The theoretical framework developed originally for modeling nonlinear Rayleigh waves in isotropic elastic half-spaces [Zabolotskaya, J. Acoust. Soc. Am. 91, 2569 (1992); see also Knight et al., ibid. 102, 1402 (1997)] has been extended to encompass a broad class of nonlinear surface wave problems. The theory is based on Hamiltonian mechanics, in which spatial Fourier amplitudes are used as generalized coordinates, and coupled spectral equations are obtained for the harmonic amplitudes in the wave. The nonlinearity coefficient matrices are expressed explicitly in terms of the second- and third-order elastic moduli of the materials. Solutions of the equations describe harmonic generation, waveform distortion, and shock formation not only at the interface but also in the interior of the solid. Cylindrical spreading and beam diffraction may be taken into account, as can transient effects in pulses. Model equations, and simulations of nonlinear surface waves in real materials, shall be presented for Rayleigh, Stoneley, Scholte, and Lamb waves, and surface waves in crystals and piezoelectric materials. The validity of the theory has been demonstrated via quantitative agreement with measurements of laser-generated Rayleigh wave pulses with shocks in fused quartz [Lomonosov et al., J. Acoust. Soc. Am. 101, 3080(A) (1997)]. [Work supported by NSF and ONR.]
Repulsion phenomena in the phase-velocity dispersion curves of circumferential waves on elastic cylindrical shells
Authors: Maze G. , Léon F. , Ripoche J. , Überall H.
Published: July 2002

The complex eigenfrequencies of a fluid-immersed evacuated infinite cylindrical shell, when plotted in the complex frequency plane, can be grouped into families corresponding to different types of circumferential waves. The dispersion curves versus frequency of the phase velocities of these circumferential waves are analogous to those of the Lamb waves on a plate A0, A1,… and S0, S1,…, but contain an additional branch reminiscent of the fluid-borne Scholte–Stoneley wave. This branch together with the A0-analog forms an interacting pair of dispersion curves A0+ (upper branch) and A0− (lower branch) which exhibit a repulsion phenomenon near the ambient fluid sound speed. Results of a recent numerical study of this phenomenon are here explained by perturbation theory, showing that during repulsion the wave character gets exchanged so that at frequencies above repulsion A0+ is a flexural and A0− a fluid-borne wave, and vice versa below repulsion.
Resolution of front–back ambiguity in spatial hearing by listener and source movement
Authors: Wightman Frederic L. , Kistler Doris J.
Published: July 2002

Normally, the apparent position of a sound source corresponds closely to its actual position. However, in some experimental situations listeners make large errors, such as indicating that a source in the frontal hemifield appears to be in the rear hemifield, or vice versa. These front–back confusions are thought to be a result of the inherent ambiguity of the primary interaural difference cues, interaural time difference (ITD) in particular. A given ITD could have been produced by a sound source anywhere on the so-called “cone of confusion.” More than 50 years ago Wallach [J. Exp. Psychol. 27, 339–368 (1940)] argued that small head movements could provide the information necessary to resolve the ambiguity. The direction of the change in ITD that accompanies a head rotation is an unambiguous indicator of the proper hemifield. The experiments reported here are a modern test of Wallach’s hypothesis. Listeners indicated the apparent positions of real and virtual sound sources in conditions in which head movements were either restricted or encouraged. The front–back confusions made in the restricted condition nearly disappeared in the condition in which head movements were encouraged. In a second experiment head movements were restricted, but the sound source was moved, either by the experimenter or by the listener. Only when the listener moved the sound source did front–back confusions disappear. The results clearly support Wallach’s hypothesis and suggest further that head movements are not required to produce the dynamic cues needed to resolve front–back ambiguity.
Interarticulator phasing, locus equations, and degree of coarticulation
Authors: Löfqvist Anders
Published: July 2002

A locus equation plots the frequency of the second formant at vowel onset against the target frequency of the same formant for the vowel in a consonant–vowel sequence, across different vowel contexts. It has generally been assumed that the slope of the locus equation reflects the degree of coarticulation between the consonant and the vowel, with a steeper slope showing more coarticulation. This study examined the articulatory basis for this assumption. Four subjects participated and produced VCV sequences of the consonants /b, d, g/ and the vowels /i, a, u/. The movements of the tongue and the lips were recorded using a magnetometer system. One articulatory measure was the temporal phasing between the onset of the lip closing movement for the bilabial consonant and the onset of the tongue movement from the first to the second vowel in a VCV sequence. A second measure was the magnitude of the tongue movement during the oral stop closure, averaged across four receivers on the tongue. A third measure was the magnitude of the tongue movement from the onset of the second vowel to the tongue position for that vowel. When compared with the corresponding locus equations, no measure showed any support for the assumption that the slope serves as an index of the degree of coarticulation between the consonant and the vowel.
Consonant recordings for speech testing
Authors: Shannon Robert V. , Jensvold Angela , Padilla Monica , Robert Mark E. , Wang Xiaosong
Published: July 2002

Initial and medial consonants were recorded in three vowel contexts for use in speech recognition experiments. Five male and five female talkers were recorded producing the twenty-five consonants /b,d,g,p,t,k,m,n,ŋ,l,r,f,v,θ,ð,s,z,∫,t∫,dȝ,ȝ,j,w,ʍ,h/ in medial (v/C/v) and initial (C/v) positions using vowels /a/ (“hod”), /i/ (“heed”), and /u/ (“who’d”). The sampling rate for these recordings was 44.1 kHz. Representative tokens of each consonant were amplitude normalized to the steady-state portion of the vowel. Listening tests were conducted with normal-hearing listeners on a subset of twenty consonants in all three vowel contexts and in initial and medial positions. The results showed that the consonants were clearly recognized with only a few minor confusions, primarily between /v/ and /ð/. The full set of recordings is available for research use.
Speech recognition with reduced spectral cues as a function of age
Authors: Eisenberg Laurie S. , Shannon Robert V. , Schaefer Martinez Amy , Wygonski John , Boothroyd Arthur
Published: July 2002

Adult listeners are able to recognize speech even under conditions of severe spectral degradation. To assess the developmental time course of this robust pattern recognition, speech recognition was measured in two groups of children (5–7 and 10–12 years of age) as a function of the degree of spectral resolution. Results were compared to recognition performance of adults listening to the same materials and conditions. The spectral detail was systematically manipulated using a noise-band vocoder in which filtered noise bands were modulated by the amplitude envelope from the same spectral bands in speech. Performance scores between adults and older children did not differ statistically, whereas scores by younger children were significantly lower; they required more spectral resolution to perform at the same level as adults and older children. Part of the deficit in younger children was due to their inability to utilize fully the sensory information, and part was due to their incomplete linguistic/cognitive development. The fact that young children cannot recognize spectrally degraded speech as well as adults suggests that a long learning period is required for robust acoustic pattern recognition. These findings have implications for the application of auditory sensory devices for young children with early-onset hearing loss.
Non-Newtonian Flow through Porous Media. II. Experimental
Authors: Sadowski Thomas J.
Published: July 2002

In the study of the flow of shear-sensitive fluids through porous media, fourteen different aqueous solutions of polyethylene glycol, polyvinyl alcohol, and hydroxy-ethylcellulose were investigated. The shear-sensitive viscosities of these fluids were characterized by the three-parameter Ellis model. Two different types of flow behavior were observed: (1) When the volumetric flow rates were held constant, the results were both steady and reversible. The flow data were successfully correlated by a modified Darcy's law. It is shown that the characteristic time of the fluid can be used to designate regions of behavior where elastic effects are important. (2) When the pressure drop across the porous medium was held constant, the results were both unsteady and irreversible. In this case, polymer adsorption and gel formation were believed to have occurred throughout the bed.
An Activated-State Model for Clay Suspension Rheology
Authors: Dawson Rapier
Published: July 2002

An activated-state model for the flow of aqueous bentonite suspensions has been used to match rheology data taken over a wide range of temperatures and shear rates. The parameters used in the theory all have physical significance and their values are consistant with estimates made independently. The activated state for clay flow appears to be the state where the clay plates are parallel and just passing each other. The main barrier to activation is the loss of rotational entropy associated with this alignment of the plates.
A Path-Dependent Variable Approach to Nonlinear Viscoelastic Behavior
Authors: Kinder D. F. , Sternstein S. S.
Published: July 2002

The theoretical and experimental existence of transient strain responses which result from nonlinear interactions between loads applied at different times to viscoelastic materials with fading memory is demonstrated. A theory which retains the simplicity of a single-integral model and yet which is capable of modeling transient strain responses is proposed. The theory is used to analyze some previously published data on poly(vinyl chloride), poly-(methyl methacrylate), polyethylene, and polyurethane.
Viscosity equation for concentrated suspensions of charged colloidal particles
Authors: Ogawa A. , Yamada H. , Matsuda S. , Okajima K. , Doi M.
Published: July 2002

Concentrated suspensions of charged stabilized colloidal particles exhibit very large viscosity at low shear rate, a strong shear-thinning behavior at intermediate shear rate, and a constant second Newtonian viscosity at high shear rate. This type of non-Newtonian behavior is affected by many factors such as the particle volume fraction φ, the particle diameter, the surface electric potential ψ0, salt concentration, etc. The generalized equation for the viscosity η of this system is proposed by applying Eyring’s transition state theory. The surface electric potential ψ0 and the thickness of the electric double layer κ−1 are determined by applying the theory to experimental data. Systematic experiments of η of the model colloidal dispersion systems are carried out as the function of φ and shear rate and the results are satisfactorily reproduced by the present theory. The effects of hydrodynamic diameter dh and ψ0 of the colloidal particle on η are also quantitatively explained.
Anode Micro Model of Solid Oxide Fuel Cell
Authors: Chan S. H. , Xia Z. T.
Published: July 2002

This paper presents the work on the development of a micro model of a solid oxide fuel cell (SOFC) porous anode, which formed by the mixture of electronic and ionic conductors. The model establishes the complex relationship between the transport phenomena, which includes the transports of electron, ion and gas molecules through the electrode and the electrochemical reaction at the three-phase boundary of the electrode. All forms of polarization losses were considered. Results show that, in general, the smaller the particle size in the anode microstructure, the larger the active area favorable to electrochemical reaction will be and thus lowering the overall polarization. However, the concentration polarization will likely play an important role, in particular for a thick electrode, if the particle size is smaller than certain limit causing substantial increase in flow resistance. The overall polarization reaches a minimum at certain particle size. In addition, it is known that the water vapor content in the hydrogen can greatly influence the polarization but the proper amount of water required for a particular anode design was not well researched, despite its importance. In this study, it was found that very high anode polarization is achieved when pure hydrogen is used. The polarization drops significantly when a small amount of water vapor is added in the hydrogen and the polarization does not change greatly in a wide range of water vapor partial pressure. Finally, there is a strong link between the anode thickness and particle size in anode design. The bigger the particle size in the anode microstructure, the thicker the anode should be for providing sufficient reaction sites. © 2001 The Electrochemical Society. All rights reserved.
In Situ X-Ray Absorption Near-Edge Structure Study of the Active and Transpassive Dissolution of Passive Films on Ni and Ni-Cr Alloys in 0.1 M  H 2 SO 4
Authors: Oblonsky Lucy J. , Ryan Mary P.
Published: July 2002

The formation, reduction, and dissolution processes of passive films formed on Ni, Ni-9 atom % Cr, and Ni-18 atom % Cr alloys in deaerated pH 2, 0.1 M sulfuric acid were studied using in situ X-ray absorption near-edge structure during potential stepping from passive to cathodic or transpassive potentials. At passive potentials, Ni slowly dissolves from pure Ni and Ni-9 atom % Cr, while Cr from the Ni-9 atom % Cr alloy does not dissolve. At passive potentials, neither Ni nor Cr from the Ni-18 atom % Cr alloy dissolves. Stepping between passive and cathodic potentials results in the loss of Ni and Cr to different extents, depending upon the Cr content. No Ni dissolves from either the Ni or the Ni-Cr alloys when the potential is first stepped from the passive to the cathodic potential. Oxidized Ni is reduced to Ni metal in a solid-state reduction reaction. However, upon stepping the potential back to the passive range, Ni does dissolve, with the amount of Ni lost decreasing as Cr content increases: significant Ni dissolves at 0% Cr, a small amount dissolves at 9 atom % Cr, and almost no Ni dissolves at 18 atom % Cr. In contrast, for both the Ni-Cr alloys, approximately a monolayer of Cr dissolves during the step from passive to cathodic potentials, while no Cr dissolves when the potential is stepped back to the passive range. In pH 2 sulfuric acid, Cr in Ni-Cr alloys is susceptible to reductive dissolution but not active dissolution. Transpassivity was also explored. For pure Ni, transpassive dissolution begins above +0.4 V referenced to mercurous sulfate electrode (MSE) and becomes rapid above +0.5 V. For the Ni-Cr alloys, transpassive dissolution of both Ni and Cr begins above +0.3 V MSE, becoming rapid at +0.4 V. Although Cr provides protection to Ni from active dissolution and from dissolution at passive potentials, Ni does not protect Cr from dissolution at transpassive potentials. © 2001 The Electrochemical Society. All rights reserved.
Micro-Raman Spectroscopic Study on Layered Lithium Manganese Oxide and Its Delithiated/Relithiated Derivatives
Authors: Hwang Seong-Ju , Park Hyo-Suk , Choy Jin-Ho , Campet Guy , Portier Josik , Kwon Chai-Won , Etourneau Jean
Published: July 2002

Micro-Raman spectroscopic analyses have been performed for the layered

LiMnO

2

compound and its delithiated/relithiated derivatives in order to probe the effect of Li extraction/insertion on the local structure around manganese ion in this layered material. For this purpose, we have first tried to establish a spectroscopic measure for identifying the lithium manganates with closely related structures. From the detailed comparison among the Raman spectra of layered and spinel-structured lithium manganates, both phases can be easily differentiated from each other by using micro-Raman spectroscopy. Based on these experimental findings, we are able to conclude that the chemical or electrochemical deintercalation of lithium gives rise to the Mn migration into the interlayer lithium site, resulting in the creation of the spinel-like cation ordering. © 2001 The Electrochemical Society. All rights reserved.