bluuebunny/crossref_metadata_2025 huggingface dataset:
Compensation for array nonidealities by electronics
Authors: Liu D.-L. (Donald) , Waag Robert C. , Oakley Clyde
Published: July 2002

Array elements usually have nonuniform characteristics in terms of element position, sensitivity, and waveform shape. Crosstalk caused by acoustic and electrical coupling limits the directivity of individual elements. These array nonidealities can be compensated by using pulser electronics with programmable transmit waveforms. Experiments were performed with a 2048-element ring transducer and a 3×3 test block for a 64×64-element 2-D array. With the ring transducer, a thin wire was suspended at the center of the ring, and single-element, pulse–echo data were collected for each element. To derive the one-way inverse response for each element, the two-way response was deconvolved using FFT, with special attention to phase unwrapping. Implementation of the inverse filtering reduced element arrival time fluctuation from 47 to 0.9 ns, energy level fluctuation from 1.2 to 0.4 dB, and increased the waveform similarity from 0.94 to 0.99. With the 3×3 test block, cancellation of crosstalk was performed by exciting neighboring elements with an opposing signal. The opposing signal was obtained by multiplying the original signal with a decoupling coefficient. Experimental results show that, with the particular test block, a decoupling coefficient of −0.08 extended the −6 dB half-angle from 10.8 to 14.8 deg, with a corresponding decrease of 4.5 dB in sensitivity.
A review of data obtained from long-range acoustic propagation experiments in the ocean
Authors: Dushaw Brian D.
Published: July 2002

Broadband acoustic propagation data have been obtained at ranges up to 5 Mm and for frequencies as low as 28 Hz. The arrival patterns measured on the sound channel axis generally have well resolved steep ray arrivals, unstable or chaotic shallow angle arrivals, and a sharp SOFAR cutoff. The wander and spread of the steep ray arrivals increase with range roughly as predicted. The effect of internal waves on the propagation are evident: In most cases the shallow-angle acoustical energy has been severely scattered by internal waves, rendering the use of these data problematical. In addition, the internal waves cause a diffusion of energy away from the sound channel axis. At 28 Hz, more stability in the arrival patterns is evident, including the shallow-angle portion. The internal waves scatter the energy associated with the earlier, resolvable ray vertically and temporally, but with less effect than on the latest acoustic arrivals. Acoustic propagation at lower frequency apparently reduces the detrimental effect of internal waves on the coherence of the signals. Acoustical receptions at very deep receivers have ‘‘ray-like’’ arrivals in the shadow zone of the predicted time front. These ‘‘ray-like’’ arrivals are associated with the cusps or caustics of the time front, but they cannot be explained by the full wave equation or by internal wave scattering.
Exact rays for problems involving ray chaos
Authors: Lingevitch Joseph F. , Collins Michael D.
Published: July 2002

Classical rays are useful for both solving problems and visualizing solutions. Exact rays [T. L. Foreman, J. Acoust. Soc. Am. 86, 234–246 (1989)] are useful for visualizing solutions that have been obtained with other techniques. When chaos arises [Smith et al., J. Acoust. Soc. Am. 92, 1939–1949 (1992)], classical rays are of limited use. Exact rays should be useful even when classical rays are chaotic. This topic is investigated using parabolic equation techniques to generate solutions to problems that exhibit ray chaos. [Work supported by ONR.]
Resonant cavity dependence of auditory-nerve fibers of the frog rana pipiens
Authors: Anderson Michael J. , Micheli-Tzanakou Evangelia
Published: July 2002

Auditory electrophysiological experiments were conducted to study the hypothesis that sound transduction by frogs is dependent on the volume of a resonant cavity, which is made up of the middle ear, Eustachian tube, and mouth. Using a closed acoustic delivery system, the extracellular responses to the interaction of a 100-ms pure tone of varying frequency and a single-cycle sinusoidal pulse were recorded from the eighth-nerve, via a ventral approach. Results show that the resonant cavity system used in vocalizing is also involved in sound transduction. When the Eustachian tube is closed, by a small piece of oiled paper or Apiezon, there is a reduction in the mean spike count of the eighth-nerve fibers. Removing the occlusion restores the firing rate to normal levels. This information, together with knowledge of the fibers’ best excitatory frequency (BEF) and inhibitability, is important because it provides insight into the peripheral origin (i.e., Amphibian papilla, Basilar papilla, or Sacculus) of the nerve fibers. Since some nerve fibers respond by phase locking to the stimulus, taking the FFT of the response also improves our understanding of sound transduction methods employed by the inner ear apparatus. [Work supported by NIH predoctoral fellowship GM17890 to MA.]
Auditory filter shapes in the budgerigar (Melopsittacus undulatus) derived from notched-noise maskers
Authors: Lin Jian-Yu , Dooling Robert J. , Dent Michael L.
Published: July 2002

Estimates of the filter bandwidths in the avian auditory system have traditionally come from either single-unit tuning curves or psychophysical masking studies using broad (critical ratio) or narrow (critical band) noises—procedures that are known to have certain limitations. The experiment reported here used the notched-noise method for determining the size and shape of the auditory filter at 2.86 kHz—the center of the budgerigar’s range of hearing. Three budgerigars were trained by operant conditioning to detect a pure tone in a background of continuous noise and tested daily until thresholds stabilized. Masked thresholds were then obtained for noises of eleven different notch widths (five symmetric, six asymmetric) surrounding 2.86 kHz. Relative equivalent rectangular bandwidths were evaluated using several procedures and these bandwidths were compared to other estimates of filter bandwidths in the budgerigar auditory system from critical ratios, directly measured critical bands, critical modulation frequency, psychophysical tuning curves, and the detection of gaps in pure tones. The size and shape of filter bandwidths in budgerigars will be compared to similar measures on other birds and other vertebrates. [Work supported by NIH Grant Nos. DC-00198 and MH-00982 to RJD.]
Central auditory processing in a patient with malignant glioma
Authors: Daly D. M.
Published: July 2002

In brain gliomas infiltrate white matter, compressing or destroying axons en passant. Such tumors rarely invade cortex; they alter local blood flow and cellular metabolism and produce seizures by corticopedal disruption and deafferentiation. The case of a 15-yr-old girl who developed complex partial seizures (daze, mastication) at 13 yr is reported. EEG disclosed left anterior temporal and right mesial temporal foci. An unorthodox occipital approach removed a grade IV astrocytoma deep within the left temporal region, sparing auditory and visual functioning. The patient was tested with four sets of synthesized sounds [D. M. Daly et al., J. Neurophysiol. 44, 200–222 (1980)]. Pre-op auditory functioning was intact with vowels, BDG, and BW. Performance on GY was aberrant but better than chance with right ear (AD)/hand, right ear/left hand, and left ear (AS)/right hand, but nearly normal with left ear/hand; typically AD boundary increased >10 ms; AS decreased <15 ms. Post-operatively GY performance improved tenfold (LRCS). At one year, cumulative AD performance was diminished only by brief fixed-response episodes; at 2 yr performance was within normal limits. Results demonstrate distant electrographic foci resolved and performance improved over a considerable time once malignant irritative source was removed.
Frequency weighting functions for nonsense syllable test speech materials as estimated by a correlational method
Authors: Turner Christopher W. , Tanaka Chiemi , Knapp Jennifer , Kwon Bomjun
Published: July 2002

A correlational method [K. A. Doherty and C. W. Turner, J. Acoust. Soc. Am. 100, 3769–3773 (1996)] was used to estimate the relative weights of four frequency bands for the 258-item UCLA nonsense syllable test in ten normal-hearing listeners. Random levels of corresponding bandpass noise were added to the speech tokens on each trial. From the trial-by-trial data, correlations between the noise level and listener’s performance yielded an estimate of the relative weight placed upon each band. The weighting functions were very similar across all listeners. This procedure appears to be a simple, fast, and reliable method for measuring speech recognition frequency weighting functions in individual subjects. The correlational weighting function showed differences from the frequency importance function derived using traditional articulation index (AI) filtering experiments. Some speech bands that were shown to contain significant speech information by the AI methods were not highly weighted when all four bands were presented to the listeners in the correlational procedure. It is hypothesized that these differences reflect the way in which listeners use speech information that is redundant across frequency regions. [Work supported by NIDCD.]
Sound velocity measurement in sub-wavelength thick samples
Authors: Yuan X. , Cao W.
Published: July 2002

A conflict exists in ultrasonic measurements between the resolution, which requires higher frequency, and the penetration depth, which requires long wavelength. The traditional pulse–echo method for sound velocity measurement fails when the sample becomes too thin to allow the separation of repeated echoes. A signal processing scheme in frequency domain is described here to maximize the resolution of broadband transducers. The Wiener optimum filtering factor is used, together with the multiple sampling average technique, for power spectrum calculation. Using a broadband 2-MHz center frequency ultrasonic transducer, the sound velocity was successfully measured in brass shims as thin as 5% of the wavelength λ.
Validity and implications of ray-based studies for long-range propagation through internal waves
Authors: Simmen Jeffrey A. , Flatte Stanley M. , Wang Guang-Yu
Published: July 2002

An analysis of the effects of ocean internal waves on long-range propagation is presented from a geometrical-optics point of view, and the validity of this ray-based approach is discussed. It is concluded that in the presence of internal waves, the observed depth diffusion of energy in the late-arriving portion of the timefront is primarily a result of refraction (not diffraction) due to chaotic rays. It is found that internal waves can cause a single eigenray to break up into several microrays having upper turning points spread 10 km horizontally and 100 m vertically, affecting the resolution of ocean acoustic tomography. The validity of ray-based, semi-classical waveforms to represent received arrivals is evaluated by comparing waveforms generated with parabolic-equation simulations: The semi-classical waveforms reproduce the correct arrival time and temporal shape of almost all arrivals, even those that are made of dozens of microrays induced by internal waves. [Work supported by ONR.]
Sound radiation by flat layered structures
Authors: Lyamshev Leonid M.
Published: July 2002

Sound radiation by flat layered structures oscillating under the effect of random fractal forces has been investigated theoretically. The reciprocity theorem formulated earlier by the author has been used and the boundary problem solution is put down in an integral form. It is demonstrated that an acoustical pattern in the far wave field is determined by the product of the structure transmission coefficient and the Fourier spectrum of external forces. Random fractal forces are characterized by a correlation function of mass fractal dimension. It has been established that the fractal dimension of average intensity of acoustic field fluctuations coincides with the fractal dimension of the forces. Single-layer (a thin plate), double-layer, and triple-layer elastic structures are considered. It is noted that the singularity spectrum of an acoustic field radiated by a wall in a turbulent flow coincides with the singularity spectrum of wall pressure fluctuations. [This research is supported by the Russian Foundation for Basic Research.]
Mapping climatic temperature changes in the ocean with acoustic tomography: Navigational requirements
Authors: Spiesberger John L. , Fabrikant Anatoly L. , Silivra Anisim A. , Hurlburt Harley E.
Published: July 2002

In eddy-resolving hydrodynamic models, first-mode baroclinic Rossby waves linked to El Niño/Southern Oscillation are the dominant features which change basin-wide temperatures below the seasonal thermocline in the northeast Pacific at periods less than a decade. Realistic simulations are carried out in which Rossby waves are mapped using acoustic tomography. Based on the model which propagated these waves, a Kalman filter is used to map temperature signals for a year. At 300-m depth, 80% of the model variance is accounted for with tomography when the navigational errors of the sources and receivers are as poor as 1 km. Consequently, it may be unnecessary to accurately navigate actual tomographic instruments to map climate change [Spiesberger et al., IEEE Ocean. Eng. 22 (1997)]. [Work supported by SERDP and ONR.]
A critique on modeling absorbent materials from a numerical simulation perspective
Authors: Basu Debashis
Published: July 2002

Absorbent materials, poroelastic in nature, have very complex acoustic wave propagation characteristics in terms of the physics and mathematics defining the phenomenon. Even for a single layer of absorbent, the mathematics governing the physics of the material under acoustic flow conditions is quite daunting. A critical review of the progress in the theories (and inherent assumptions) is being presented. Proper engineering judgment might allow a more simplified numerical simulation to get an idea of the complex acoustical behavior. More often it is the lack of availability of proper data which drives the numerical simulation to be done under certain inexact approximations. The present article tries to lay down the theories and semi-empirical relations developed over the past few decades, and assumptions allowing a simplified model, which at least help in the acoustic characterization of a complex problem. With growing emphasis on a ‘‘better, safer, quieter’’ acoustic environment and mandatory noise control measured in different countries, there would be an ever increasing demand for effective acoustic design and absorbent materials would play a key role in several applications. As would be clearly apparent from the current article, the available ‘‘standard commercial’’ data on absorbent materials gives an estimate of what is happening but does not contain enough information to accuratelypredict the physics of the problem in certain situations.
Effects of an audience and variable architectural features on the acoustics of Boettcher Concert Hall
Authors: Madaras Gary , Bradley John S. , Jaffe Christopher
Published: July 2002

Acoustic parameters (including reverberation time, early decay time, relative sound level, early to late sound ratios, lateral energy fraction, and interaural cross correlation) have been measured in Boettcher Concert Hall. All parameters were measured using different settings of variable architectural features such as acoustic drapes, variable height overhead stage reflectors, and movable stage towers. The monaural parameters were also measured with and without an audience. The effects of the variable features on the acoustic parameters are assessed. The effects of the audience on some of the acoustic parameters have been estimated using standard calculation methods. Calculated differences are compared to those actually measured in the hall. [Work supported by the Concert Hall Research Group.]
Measurement of the echo location signals of the Atlantic Spotted Dolphin Stenella frontalis in the waters off the Grand Bahamas
Authors: Au Whitlow W. L. , Herzing Denise L.
Published: July 2002

A line array of three hydrophones with a video camera attached to the array was used to measure the echo location signals of wild Atlantic Spotted Dolphins. The separation distance between hydrophones in the array was 30 cm. The array was attached to a float that supported an amplifier–line driver assembly with the signals sent via a 76-m multi-conductor cable back to the support boat. The float and array assembly was oriented by a swimmer. The echo location signals from the hydrophone were digitized simultaneously at a sample rate of 500 kHz. Twenty files of echo location click trains were collected with the quality of the data varying from poor (files with lots of whistles and off-axis signals) to very good. The on-axis signals typically had a bimodal spectrum with a low-frequency peak at 45–60 Hz and a high-frequency peak at 120–140 kHz. Peak-to-peak source levels up to 210 dB re: 1 μPa were measured. The rms bandwidth varied between 32 and 46 kHz, with a cluster around 40 kHz.
Effects of reed cell geometry on the vibration frequency and spectrum of a free reed
Authors: Cottingham James P.
Published: July 2002

In a reed organ the free reed is mounted above the windchest and is typically surrounded by a reed cell cavity with small cross-sectional area. The length of this tubelike cavity varies from just slightly longer than the reed in some instruments to several centimeters longer in others. A series of measurements of the frequency and spectrum of the radiated sound have been made on reeds from American reed organs mounted on a laboratory windchest, using a simulated reed cell of varying dimensions. The presence of the reed cell cavity generally results in a lower frequency of vibration at the same blowing pressure and increased amplitudes of the higher harmonics relative to the fundamental, although some anomalous effects are observed for longer reed cells. Some hysteresis effects are observed as the blowing pressure is continuously increased and decreased.
Investigation into the feasibility of a smart acoustic guitar
Authors: Griffin Steven F. , Hanagud Sathya V.
Published: July 2002

In 1990, the ‘‘Mendelssohn’’ Stradivarius violin sold for $1,686,700. A good violin sells for around $2000. What is it about the Stradivarius that makes it cost almost 1000 times as much? The structure and geometry of the two instruments are similar, yet subtle differences in structural dynamics cause them to vibrate differently in response to a violinist’s bow. This, in turn, causes differences in the sound produced by the two instruments, which ultimately determines quality and, to a large extent, price. If it were possible to force the less expensive violin to vibrate like the Stradivarius, the legendary sound would follow. This paper explores the potential for the use of active structural/acoustic control to obtain a desired acoustic response in an acoustic guitar. Detailed information on the desired acoustic response of guitars is available, and experimental specimens are relatively easy to obtain. The model developed is an elastic plate with piezoceramic sensors and actuators backed by a rigid, vented cavity. The sensors and actuators are used with active feedback control to influence the vibration and acoustics of the guitar. The feasibility of favorably changing acoustic guitar vibration and acoustics is examined in detail, including analytical and experimental results.
Coupled phase theory for the complex density of rigid-porous materials
Authors: Attenborough Keith , Evans Jon
Published: July 2002

Despite the fact that most porous materials, of influence in building and urban acoustics, are either fibrous or granular in nature, theoretical models used to predict their acoustical behavior at audio frequencies are derived from an assumed pore-based microstructure. This leads to the need for pore-related parameters that are either difficult to measure or not measurable independently. An alternative is to start from the known size and shape distribution and properties of the constituent solid particles. One possible particle-based approach is coupled phase theory. This has been used extensively to predict sound propagation in suspensions and emul sions. By means of an expression for the interphase inertial force appropriate to spherical particles, it has been shown that ‘‘frameless’’ Biot theory is equivalent to coupled phase theory modified to include hydrodynamic interactions between the forces acting on individual particles. The two models differ only in their expression of the interphase viscous force. Extensions of the coupled phase approach that are necessary when considering air-filled granular and fibrous materials are discussed.
Range of performance for two tasks with random-frequency context tones
Authors: Neff Donna L. , Kessler Christina J. , Sadralodabai Toktam , Gleason Traci R.
Published: July 2002

Forty listeners were tested on two tasks known to show large individual differences in performance. In one task, termed sample discrimination, pairs of target tones were drawn from each of two overlapping frequency distributions, and listeners indicated which pair came from the higher distribution. Target tones were presented alone and in the presence of two flanking context tones that were either fixed at 500 and 4000 Hz or had Gaussian variation centered at these two frequencies. In the second task, masked thresholds were determined for a 1000-Hz tone in the presence of ten-component, random-frequency, simultaneous maskers. The maskers were drawn on each presentation from a pool of either 200 or 10 waveforms. For sample discrimination, the range of performance was large for both the no-context and fixed-frequency context conditions. For the Gaussian-context condition, few listeners exceeded chance performance. Significant effects of testing order were found, with exposure to Gaussian-context conditions degrading later performance. For masking, performance did not differ for large versus small waveform pools, and the 35-dB range of performance corroborated previous work. For both tasks, random-frequency context degraded performance for the majority of listeners. [Work supported by NIDCD.]
Bandwidth of spectral resolution for the ‘‘C-O-G’’ effect in vowel-like complex sounds
Authors: Xu Qiang , Feth Lawrence L. , Anantharaman Jayanth N. , Krishnamurthy Ashok K.
Published: July 2002

Several investigators [e.g., Chistovitch et al. (1979); Carson et al. (1975); Beddor and Hawkins (1990)] report that listeners match an adjustable single-formant to the spectral center of gravity of a two-formant signal, as long as the two formants are separated by 3.5 Bark or less. This suggests that listeners use some form of spectral averaging in processing vowel sounds. Assmann’s 1991 results do not confirm the C-O-G predictions. The preliminary work [Feth et al. (1996)] used the double-staircase procedure to confirm the C-O-G effect for two-formant complex sounds using both periodic pulse train and white noise excitation of the filter used to generate the signals. In the work to be reported here, the relationship between the C-O-G effect and an independent measure of spectral resolution is explored. In 1977, Feth and O’Malley used two-component complex tones described by Voelcker (1966) to estimate spectral resolving power. Resolution bandwidths paralleled the growth of the critical bandwidth with center frequency, but were 2.5–3 times wider. For the same listeners, the limit of spectral averaging for the C-O-G effect and the resolution bandwidth using Voelcker tone pairs have been measured. These results will be compared with predictions of an IWAIF model. [Work supported by a grant from AFOSR.]
Further examination between the relationship of auditory filter bandwidth and temporal resolution
Authors: Strickland Elizabeth A.
Published: July 2002

In a previous paper, the relationship between auditory filter bandwidth and temporal resolution was examined in the context of an envelope detector model [E. A. Strickland, J. Acoust. Soc. Am. 97, 3330(A) (1995)]. This model predicts that temporal resolution will be limited by peripheral filtering at low frequencies, and by a central limitation at high frequencies. In the previous paper, time constants as measured by temporal modulation transfer functions (TMTFs) were compared to time constants predicted from the 3-dB bandwidths of auditory filters, for TMTFs and filters measured as a function of frequency region and level. Time constants for the TMTFs covaried with those estimated from the filters for low frequencies and levels, but were constant at high frequencies, as predicted. In the present paper, the auditory filters were used in the first stage of the envelope detector model, and TMTFs predicted by the model were compared to measured TMTFs. Time constants for the TMTFs increased as frequency decreased, but not as much as was predicted by the model. The model predicts time constants well for high frequencies, where the limitation is central. [Work partially supported by a post-doctoral fellowship from NIH.]
Mundane issues in active classification for naval purposes
Authors: Goldsberry Tommy G.
Published: July 2002

The recent revolution in computational capability, combined with finite-element analysis techniques, has greatly expanded the ability to analyze vibrational modes of simple and complex structures and acoustic radiation from these structures. These developments have encouraged belief that one may be able to categorize or classify complex structures of interest to the U.S. Navy (e.g., submarines, mines, or swimmers) by analysis of the acoustic energy reflected and reradiated from such structures (echo structure). A detailed discussion of this topic is beyond the scope of this meeting. However, academic researchers wishing to obtain support for their research may benefit from some discussion of the importance of practical limitations such as finite transducer bandwidth, multipath propagation, and population densities on the relevance of classification methods for naval purposes. Some of these issues will be discussed in this presentation.
Meridional leaky ray amplitudes for tilted cylinders and high-frequency backscattering enhancements for finite cylinders
Authors: Marston Philip L.
Published: July 2002

Consider the meridional plane which contains the axis of a circular cylinder and the incident acoustic wave vector. The meridional leaky rays which lie in this plane may be excited for certain tilt angles. Radiation resulting from the reflection of such rays off truncations on a cylinder gives strong high-frequency backscattering enhancements [Kaduchak et al., J. Acoust. Soc. Am. 100, 67–71 (1996)]. The present work gives ray approximations for such backscattering contributions and for the related contributions to scattering by tilted infinite cylinders. These are evaluated using a general convolution integral formulation [P. L. Marston, J. Acoust. Soc. Am. 100, 2820(A) (1996)]. The infinite cylinder results for radiation by Rayleigh waves on a solid cylinder agree with the partial-wave series solution. The truncation enhancement for a finite cylinder causes a backward-directed three-dimensional wavefront possessing a vanishing Gaussian curvature. The amplitude from the far-field propagation integral associated with the caustic due to this wavefront can significantly exceed the amplitude for reflection off a rigid sphere having the same radius as the cylinder. The analysis does not rely on thin shell assumptions. [Work supported by the Office of Naval Research.]
Scattering and attenuation of an elastic wave by a viscoelastic cylinder. II. SV-wave incidence
Authors: Liu Yin-Bin , Ying Chong-Fu
Published: July 2002

The scattering and attenuation of a shear wave by a circular, elastic cylinder with and without intrinsic attenuation are investigated. The analytical solutions for scattered and internal fields caused by a normally incident plane SV wave are derived. Resonance scattering, radiation pattern, scattering cross section, and synthetic seismogram are calculated. The calculated synthetic seismograms show that the creeping (diffraction) waves include the shear creeping wave S1Ŝ1S1 and exciting (or converting) compressional creeping wave S1P̂1P1. The creeping waves propagate on the surface outside the media and depend mainly on the outside media, and are little affected by the cylinder−absorbing property. The total fields are the superposition of the geometrically transmitted waves (S1P2P1, S1S2P1, and S1S2S1) which go through the cylinder and creeping waves (S1Ŝ1S1 and S1P̑1P1) which propagate on the elastic side of the elastic–cylinder interface. The first arrivals within the shadow zone are a diffraction wave S1P̑1P1 for a low-velocity inclusion and a transmitted wave S1P2P1 for a high-velocity inclusion. [Work supported by NSF of China.]
Word recognition skills of children with phonological disorders
Authors: Edwards Jan , Munson Benjamin , Fox Robert A.
Published: July 2002

There has been little research on word recognition skills of phonologically disordered children, although recent work has shown they tend to perform more poorly than age peers on phoneme-identification tasks using synthetic speech stimuli. Six phonologically disordered preschool-aged children and six typically developing controls were asked to identify CVC words in which either the final consonant or the medial vowel had been removed in steps. The stimuli were digitized natural productions of familiar words. For the silent-center task, the phonologically disordered children were significantly less accurate than peers for the two conditions with the least acoustic information. For the gating task, the phonologically disordered children were significantly less accurate than peers for the two conditions with the most acoustic information. They were less accurate than peers at identifying digitized words with no acoustic information deleted, although they were not less accurate with live voice. This suggests that perceptual representation of final consonants for the phonologically disordered children is so fragile that even such a small degradation as a reduction in bandwidth affects their performance. Divergent patterns of group differences for the two tasks are probably related to differences in the nature of acoustic cues for medial vowels and final consonants.
Mid-frequency synthetic aperture sonar imaging
Authors: Rolt Kenneth D. , Edelson Geoffrey S. , Gillespie Bradford W. , Celuzza Stephen A. , Abbot Philip A. , Gedney Charles J.
Published: July 2002

A detailed review of many temporal stability and spatial coherence experiments is used to develop a reasonable model for the temporal and spatial limitations on mid-frequency synthetic aperture sonar (SAS) in shallow water. A comparison of deep- versus shallow-water coherence experiments is made based on an extensive review of the literature. This comparison reveals that the spatial limits for arrays often dominate over temporal limits. The upper bounds on real or synthesized array lengths in shallow water that result from this analysis are presented. The feasibility of mid-frequency SAS imaging in shallow water is shown, and the predicted resolution in range, azimuth, and depth is compared to the theoretical values for a perfectly stable ocean and precise motion compensation. As a first step to validate the spatial and temporal limitation analysis, a mid-frequency surface sonar is modeled to create artificial data for SAS imaging in shallow water. The modeled environment includes a time varying ocean surface and sound-speed profiles, bottom roughness, penetration, and scattering. Useful SAS imaging is shown. [Work supported by NUWC.]
Passive synthetic aperture sonars, revisited
Authors: Sullivan Edmund J. , Carey William M.
Published: July 2002

Experimental and analytical studies have clearly shown the feasibility and applicability of passive and active synthetic aperture sonars (SAS). These investigations have spanned the infrasonic to ultrasonic frequency range. However, passive SAS has not gained widespread use due to three arguments. The first is based on a single hydrophone system, and knowledge of the source frequency is required for bearing estimation. However, with multiple hydrophones, both the bearing and frequency can be estimated simultaneously. The second argument claimed that there was no ‘‘new gain,’’ since the number of spatial and temporal degrees of freedom are constant. However, this analysis failed to account explicitly for the movement of the array, thereby ignoring the Doppler information. The third argument claimed that temporal coherence time ust be at least equal to the time of synthesization. This argument ignores the applicability of sequential coherence corrections. This paper will clarify and place these arguments in perspective. Experimental results and analyses showing performance improvements will be presented.
Dynamic mechanical measurements of marine mammal tissues
Authors: Fitzgerald Edwin R. , Strandberg John D. , Whitaker Brent R.
Published: July 2002

An automated measurement system for complex shear compliance, J*=J′−iJ″, shear modulus, G*=G′+iG″, and shear wave velocity and attenuation from 2 to 10 000 Hz at temperatures from −25 to 150 °C [E. R. Fitzgerald, Proc. Am. Chem. Soc. 60, 573–578 (1989); U. S. Patent 5,081,870 (1992)] has been used to determine these viscoelastic parameters for blubber and skin of several marine mammals. Excised samples from two stranded harbor seals, for which rescue efforts failed, were measured at 20 °C from 2 to 1000 Hz, at short intervals, from 1.9 to 12 h after death. Values of the elastic (J′) and viscous (J″) compliance components decreased with time after death, and showed sharp, ‘‘life-to-death’’ slope transitions at 4 to 6 h after death, as found in prior animal tissue measurements [Fitzgerald et al., J. Acoust. Soc. Am. 29, 61–64 (1957); E. R. Fitzgerald, Biorheology 12, 397–408 (1975)]. These measurements are compared with those previously reported for pilot whale and dolphin blubber [E. R. Fitzgerald and J. W. Fitzgerald, Mater. Sci. Eng. C 2, 209–214 (1995); Proc. Third Int. Conf. Intel. Mater. SPIE 2779, 83–88 (1996)]. [This work was supported, in part, by the Advanced Research Projects Agency and the Office of Naval Research.]
Modified masking period patterns as a function of frequency region and masker bandwidth
Authors: Eddins David A.
Published: July 2002

The auditory system must encode dynamic aspects of acoustic stimuli at frequencies throughout the audible spectrum. This coding is limited by the temporal resolution of the ear. Recent measures of modulation detection and temporal gap detection thresholds with narrow-band noises of fixed bandwidth indicate that temporal resolution does not vary with noise carrier frequency from 500 to 4400 Hz. The present study investigated temporal processing using a modified masking period pattern technique. Masked thresholds were measured for pure tones of 500, 2000, and 4000 Hz that were 400 ms in duration. Maskers consisted of narrow-band noises centered on the signal frequency that were either unmodulated or sinusoidally amplitude modulated (modulation depth=1.0) at frequencies from 4 to 256 Hz. The noise bandwidth ranged from 200 to 1600 Hz at each center frequency. By comparing masked thresholds for the unmodulated and amplitude modulated noises, one may assess both within-channel (narrowband noises) and across-channel (wideband noises) temporal processing. Preliminary results indicate that thresholds for a given masker bandwidth depend strongly on modulation frequency but vary little with signal frequency over the range tested. The data will be discussed relative to measures of temporal resolution and comodulation masking release.
Ultrasonic study of vortex viscosity and phase transitions in YBa2Cu3O7 single crystals
Authors: Dasgupta D. , Hucho C. , Feller J. R. , Sarma B. K. , Levy M.
Published: July 2002

A novel ultrasonic technique (sampled cw method) is used to probe into the viscosity of vortex systems in untwinned and twinned YBCO single crystals. Motion of the flux lines in the superconducting sample is induced via coupling with the moving ionic lattice in the bulk of the sample. Hence, the observed dissipation has its origin in the (induced) motion of the vortices with respect to the ionic background of conduction charge carriers. In the experiments which were performed, pronounced field-dependent attenuation changes were observed which are indicative of transitions from a soft vortex system at low fields to a rigid vortex system at high fields. [Research supported by Office of Naval Research and C. Hucho was supported by Deutsche Forschungsgemeinschaft.] a)Currently at: FB Physik, Augsburg, Germany.
Loudness recalibration as a function of recalibration and comparison tone level
Authors: Mapes-Riordan Dan , Yost William A.
Published: July 2002

Presenting loud tones at one frequency and quiet tones at a different frequency makes the quiet tones appear relatively louder. This phenomenon, dubbed loudness recalibration [Marks, J. Exp. Psychol. 20, 382–396 (1994)], was studied using an adaptive, two-track loudness comparison procedure. In this study, a baseline loudness comparison was initially established between two tones. Immediately following this baseline sequence, a sequence of trials were given in which the two comparison tones were preceded by a recalibration tone. The amount of steady-state loudness recalibration was measured as a function of the recalibration tone level and the baseline comparison tone level. The results showed that loudness recalibration is present when the recalibration tone level is much larger than the comparison tone level and that no loudness recalibration is generated when the recalibration tone level is less than or equal to the comparison tone level. In addition, it was found that a recalibration tone did not affect the threshold level of detection. These results support those of Marks [J. Acoust. Soc. Am. 100, 473–480 (1996)] indicating that loudness recalibration is a centrally based, fatiguelike phenomenon. [Work supported by a Program Project Grant from NIDCD.]
Positional neighborhood effects on spoken word recognition
Authors: Amano Shigeaki , Torretta Gina M. , Luce Paul A.
Published: July 2002

Previous work has shown that the composition of similarity neighborhoods has demonstrable effects on spoken word recognition. In a reanalysis of previously collected data of word identification and lexical decision, the effects of similarity neighborhoods on spoken word recognition were further explored by asking two specific questions. (1) Do neighbors at each phoneme position within a spoken word have equivalent effects on word recognition? (2) Is average neighborhood frequency or the highest neighborhood frequency the superior predictor of recognition performance? Our results show that the number of neighbors defined on the basis of initial phoneme substitution affects word recognition more than the neighbors at other phoneme positions. And, it is found that the word with the maximum frequency in a neighborhood is as good a predictor of recognition performance as the average neighborhood frequency. The implications of these findings for theories of spoken word recognition will be discussed.
Model-based signal processing in acoustics: An overview
Authors: Candy James V.
Published: July 2002

When the signal information to be extracted from a particular measurement is complex and severely contaminated with noise, then more information about the underlying physics, measurement dynamics, and noise must be incorporated into the processor. This concept defines the basic model-based approach to signal processing. Here, the development of model-based signal processing techniques applied to a diverse set of acoustic problems is discussed: (1) the extraction of sounds from a prosthetic heart valve for failure detection; (2) the enhancement of laser ultrasonic sounds in materials for nondestructive evaluation; and (3) the extraction of parameters from ocean acoustic measurements for target localization. Recall that model-based signal processing is a well-defined methodology enabling the inclusion of process, measurement, and noise models into sophisticated processing algorithms. The basic principle relies on the notion that the more information incorporated about the physics, measurements, and noise into the processor, the better (smaller error variance) the enhancement. When these parameters exactly ‘‘match’’ the process, then minimum variance can be achieved, yielding the best (in a mean-squared sense) possible results. Thus model-based processing finds its roots in minimum variance design where a cost function is investigated until it statistically yields the minimum error between predicted and measured values.
Model-based towed array processing
Authors: Sullivan Edmund J.
Published: July 2002

Model-based processing is a method of enhancing processing performance (smaller error variance) by the inclusion of physical models of the signal/medium, noise, and measurement systems into the processor. It is based on a state-space approach, which leads to Kalman type estimators. A major advantage of this approach is that it allows for the stochastic aspects of the problem to be included in a natural and self-consistent manner, thereby allowing for modeling errors to be accommodated by the processor. In this work we describe the application of model-based processing to the problem of processing towed array data. Here the focus is on four problems of interest in the field of towed array processing: (1) the bearing and source frequency estimation problem for plane waves; (2) the bearing, source frequency, and range estimation problem for the circular wavefront signal model; (3) problems (1) and (2) generalized to the case of the Rayleigh fading channel; and (4) the case of the stochastic broadband signal model. Results based on simulated data will be shown which will demonstrate the improvement in performance over conventional array processing techniques. In particular, it will be shown how this approach provides a passive synthetic aperture effect in a natural way.
Acoustic-to-articulatory mapping of isolated and intervocalic fricatives
Authors: Riegelsberger Edward L. , Krishnamurthy Ashok K.
Published: July 2002

While acoustic-to-articulatory mapping has been successful for purely voiced speech, a complete acoustic-to-articulatory mapping solution for all classes of speech sounds remains to be found. This work investigates extending acoustic-to-articulatory mapping techniques to fricative sounds. A normalized spectral correlation measure has been developed for an acoustic-to-articulatory mapping routine that produces good acoustic fits and reasonable articulatory configurations for isolated fricatives. The mapping routine can, by using this distance measure along with amplitude information, effectively separate fricative classes by place of articulation. Based on results with isolated fricatives, the acoustic-to-articulatory mapping of fricatives has been extended to the intervocalic case, where information in the voiced segments preceding and following a fricative is used to initialize its optimization. Confidence in the acoustic-to-articulatory mapping of fricatives in isolation influences how they are used in this dynamic case. Heuristics for controlling frication amplitude and mixed excitation are discussed.
An articulatory and acoustic analysis of English flaps: Evidence for attentional reduction in production
Authors: de Jong Kenneth J.
Published: July 2002

Traditional models of American English phonology include a rule that coronal stops appear as flaps before unstressed vowels. Recent studies suggest that this flapping is better explained as the result of blending the articulatory specifications for the stops with neighboring vowels. This blending produces compromise articulatory positions for the stops, which cross over the perceptual boundary between stops and flaps. This paper tests this explanation against an x-ray microbeam corpus of American English stops. The occurrence of flapping was determined via transcriptions. Regression analyses indicate that acoustic parameters such as VOT and voicing occurrence better predict transcriptions than articulatory parameters such as tongue position and motion during closure. In addition, articulatory analyses indicate a variation from [t] to flap which is generally consistent with a blending account. However, the contextual influence from the consonants on neighboring vowels and various aspects of articulatory postures in the consonants themselves is more consistent with a reduction of the stop, rather than a blending with neighboring vowels. These results suggest that flapping results from a linguistic convention which allows hypoarticulation of unstressed items and a secondary result of some of these items straying across an acoustic boundary. [Supported by the NSF and NIDCD.]
Composite transducer with spring’s structure
Authors: Jiao B. L. , Zhang J. D.
Published: July 2002

The objective of this paper is to introduce spring’s structure to a piezolaminated beam for transducer application. The stacking sequence of the plies is along the thickness and the elastoelectric conversion is through the bending modes, in which some plies are compressed while the others are stretched. The piezoelectrical equations are given under the approximation for small deflection. As an application to the receivers, the leaf and spiral springs’ structures are adapted to the numerical analysis. The acoustic impedance defined by the values in the mean is found much lower than that of the conventional transducers, while the sensitivities are significantly heightened.
Modal solution for a two-dimensional waveguide having a locally reacting wall
Authors: Logan Thomas M. , Ginsberg Jerry H. , Rogers Peter H.
Published: July 2002

Consider a two-dimensional waveguide consisting of a rigid wall and a parallel wall having uniform specific impedance. When the impedance is purely imaginary, the characteristic equation is real. In the springlike case, the eigenvalue of the fundamental mode (defined as the mode that varies most slowly in the transverse direction) is imaginary, whereas all other eigenvalues are real. This type of mode does not exist if the impedance is masslike. Morse and Ingard [Theoretical Acoustics (McGraw-Hill, New York, 1968), p. 496] fail to recognize the differing behavior of the fundamental mode for either type of lossless impedance, and subsequently no one seems to have rectified this oversight. The fundamental mode in the springlike case behaves much like the plane mode in a hard-walled waveguide in that it has no cutoff frequency, but the phase speed of this mode is subsonic at all frequencies. Introducing a resistive part to the impedance, corresponding to dissipation at the wall, moves the respective eigenvalues off the real or imaginary axis. The presentation will discuss the phase and group speeds, and the transverse mode shapes, in ideal and lossy cases.