bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement and modeling of bistatic scattering on the Florida Atlantic coastal shelf
Authors: Yamamoto Tokuo , Day Christopher , Kuru Murat
Published: July 2002

Measurements of bistatic sea floor scattering on the Fort Pierce, Florida shelf are presented. Scattering measurements have been collected using a new 32 element bilinear acoustic array. According to the volume and roughness scattering models of Yamamoto (1996) and Jackson et al. (1992), bistatic scattering depends on the bottom sediment characteristics, the interface roughness, and the incident and scattered grazing angles. Parameters for the combined volume and roughness scattering model are estimated using the observed bottom roughness and tomographically measured sediment sound speed and attenuation. Observations of bistatic scattering are compared to the combined scattering model. Good agreement between the observed and modeled scattering pattern permits an accurate mapping of mean sound speeds, attenuation, densities, and their three-dimensional spatial spectra using observations of bistatic scattering. [Work supported by ONR.]
The low-frequency radiation and scattering of sound from bubble distributions near the sea surface
Authors: Carey William M. , Roy Ronald A.
Published: July 2002

Microbubble plumes are produced when waves break and are convected to depth by the vortical wave motion. The question is, What role is played by these distributions in the production and scattering of sound near the sea surface at low frequency (LF)? Deep- and shallow-water ambient noise show dramatic increases with wave breaking. Individual wave breaking events show radiation down to 30 Hz. Tipping water-filled trough and bucket experiments show LF radiation associated with the entrainment of known bubble size distributions; suggesting that single bubbles cannot be the cause of this radiation. Microbubble distributions with void fractions greater than 0.01% act as collective monopole resonant oscillators excited by the energy of formation. Multipole expansions show the radiation is described by a modified Minnaert expression and a dipole radiation pattern (owing to the presence of the sea surface). Since the plume stays put, scattered sound would have a zero Doppler shift with ample Doppler spread. Acoustic images of the sea surface show discrete scattering events, while experiments show LF scattering from free bubble distributions. Results are shown which indicate that bubble plumes from breaking waves not only radiate but scatter LF sound. [Work sponsored by ONR.]
Three-dimensional ocean acoustics: Techniques and examples
Authors: Collins Michael D. , Couchman Luise S. , Lingevitch Joseph F. , Levy Mireille F. , Zaporozhets Andrew A.
Published: July 2002

The method of matched asymptotics can be used to solve scattering problems involving a compact object in a waveguide [M. D. Collins and M. F. Werby, J. Acoust. Soc. Am. 85, 1895–1902 (1989)]. This approach involves different asymptotic limits in different regions. In the inner region near the object, the Green’s function can be approximated by either the free-space or half-space Green’s function depending on the vertical location of the object. The inner problem is therefore the free-space or half-space scattering problem. The outer solution satisfies the three-dimensional parabolic equation. When horizontal variations in the waveguide are sufficiently gradual, the solution is asymptotic to a specular point source for ka=O(1). This approximation can be improved by including a vertical dipole correction. The three-dimensional parabolic equation has been applied to free-space scattering problems by solving the exterior problem for the scattered field directly [M. F. Levy and A. A. Zaporozhets, J. Acoust. Soc. Am. 103, 735–741 (1998)]. This approach is also useful for some waveguide scattering problems. [Work supported by ONR.]
The effect of transition slope and transition duration on vowel reduction in V1V2 complexes
Authors: Divenyi Pierre L. , Carré René
Published: July 2002

Digital V1V2 vowel pairs were generated using a cascade-parallel formant synthesizer. The duration of V1 was 100 ms and that of a completed V2 150 ms, while the duration of the transition was varied between 40 and 100 ms, depending on the condition. For each of six English V1V2 pairs (/iɑ/, /ɑi/, /iu/, /ui/, /uɑ/, and /ɑu/) 8–12 tokens were obtained by progressively cutting back the V2 portion and the vowel transition in 10-ms steps. Separately for each vowel pair, the cut-back tokens were presented to trained listeners who had to indicate their confidence level (using a 4-point scale) that the final portion of the token was, indeed, the vowel V2. Since high-confidence V2 responses were given not only to tokens that actually reached V2, we observed vowel reduction; the degree of vowel reduction (VR) was measured as the severity of the cut-back at which such a misperception occurred at a certain percent of the time. Using this measure, we determined the degree of VR for different durations and velocities of transition. In general, VR was larger for steeper transition slopes and for durations around 80–100 ms. [Work supported by NATO Office of Scientific Research, a grant from N.I.H., and the V.A. Medical Research.]
Variables controlling contrast generation in a urinary bladder model
Authors: Hwang Emma Y. , Fowlkes J. Brian , Carson Paul L.
Published: July 2002

An ultrasound system has been developed to generate microbubbles in vivo for use as ultrasound contrast agent. Possible applications include diagnosis of reflux in the urinary tract. In experiments designed to elucidate the contrast microbubble generation process, acoustic bursts (at 1.8 MHz, 125 ms) were propagated through a latex rubber balloon, modeled after a rabbit urinary bladder, containing fluids of various air and carbon dioxide saturations and concentrations of cavitation nuclei (0.198-μm-diam polystyrene particles). The peak rarefactional pressure threshold for contrast microbubble generation, as visualized with a diagnostic ultrasound system, decreased approximately a factor of 2 for increasing particle concentration from 108 to 1010 particles/cc, with the lowest threshold of 5.24 MPa. For samples with gas saturations below 50% and 1010 particles/cc, the average thresholds were at least twice as high as those of more saturated fluids (with mean threshold for saturated fluids of 6.45 MPa), and samples containing CO2 had considerably lower thresholds than respective under-saturations in air. At a fixed pressure amplitude, echogenicity tended to increase with both increasing particle concentration and gas saturation; this was more favorable for samples containing CO2. Even in a restricted-nuclei environment such as the urinary bladder, generation of vaporous cavitation should be possible; however, subsequently, abundant gas is needed to grow vaporous bubbles to persistent and imageable sizes, to assist in the diagnosis of urinary reflux.
Effect of climate upon organ tone
Authors: Thompson-Allen N. , Harrison J. M.
Published: July 2002

Woolsey Hall, Yale University, which houses the Newberry Memorial Organ is not climate controlled and some listeners have the impression that the tone of the organ varies with the seasons. The present work measured the overall SPL, and the SPL’s of the harmonics of the C’s of a number of flue and reed stops of the organ in August and March, 1996 to determine possible seasonal differences. The C’s of flue and reed stops were recorded in the hall using a calibrated microphone and digital tape recorder system. The tapes were played into a computer, using Spectraplus 4 software, and the overall SPL levels of each C together with the SPL levels of the harmonics were extracted. The overall levels of 67 out of the 76 observations of the C’s were 0.5–14 dB higher in August than in March, confirming the impression that the organ sounds louder in the summer. In 55 observations higher numbered harmonics that were present in August were absent in March. These findings are compatible with the impression that the organ sounds brighter in summer.
Ground influence on the definition of single rating index for noise barrier protection
Authors: Simón F. , Pfretzschner J. , de la Colina C. , Moreno A.
Published: July 2002

A single number rating index to qualify the acoustical protection of a noise barrier that accounts for the influence of the ground is developed. This is an extension of a previous index for semi-infinite barrier developed by Pfretzschner [Pfretzschner et al., Acust. Acta Acust. 82, 504–508 (1996)]. This index is based on the asymptotic value found for the insertion loss or the acoustic attenuation as physical magnitude, and it is uniquely dependent on the barrier, noise source, and acoustic characteristics of the ground in the source semi-space. The new index agrees well with measured data on a scale model under laboratory conditions, and a direct experimental measuring procedure could be envisaged. In this way the proposed index, which accounts for extrinsic properties (acoustical protection) of barriers, would complete the two previous indices dealing with intrinsic properties (transmission loss and acoustical absorption).
Wave-based matching-pursuits detection of submerged elastic targets
Authors: McClure Mark , Carin Lawrence
Published: July 2002

Matching pursuits is a nonlinear algorithm which iteratively projects a given signal onto a complete dictionary of vectors. The dictionary is constructed such that it is well matched to the signals of interest and poorly matched to the noise, thereby affording the potential for denoising, by adaptively extracting an underlying signature from a noisy waveform. In the context of wave scattering and propagation, there are basic constituents that can be used to construct most measured waveforms. A dictionary of such constituents is used here, in the context of wave-based matching-pursuit processing of acoustic waves scattered from submerged elastic targets. It is demonstrated how wave-based matching pursuits can be utilized for denoising as well as to effect a detector, the latter being parametrized via its receiver operating characteristic (ROC). Results are presented using measured aspect-dependent (orientation-dependent) scattered waveforms, for the case of a submerged elastic shell.
Psychophysical suppression as a function of signal frequency: Noise and tonal maskers
Authors: Lee Jungmee , Bacon Sid P.
Published: July 2002

Physiological studies have suggested that the basal region of the cochlea is more nonlinear than the apical region. To evaluate this possibility psychophysically, suppression was investigated across signal frequency (250, 500, 1000, 2000, and 4000 Hz) in a forward-masking paradigm using both noise and tonal maskers/suppressors. Masker duration was 200 ms, signal duration was 20 or 40 ms, and signal delay was 0 or 20 ms; the longer delay was necessary to eliminate potential confusion effects observed with the (narrow-band) noise masker. When using a noise masker (spectrum level of 40 dB), suppression was determined by comparing the threshold in the presence of a broadband masker with that in the presence of a critical band (ERB) masker. When using a tonal masker (masker level of 50 dB SPL, suppressor level of 70 dB SPL, with the suppressor frequency being 1.2 times the masker/signal frequency), suppression was determined by comparing the threshold in the presence of the masker plus suppressor with that in the presence of the masker alone. The magnitude of suppression was determined either by the measured change in signal threshold or by the inferred change in masker level. Regardless of how suppression was quantified, for both masker types, the amount of suppression increased as signal frequency increased up to about 1000 Hz, but then reached an asymptote or decreased somewhat as signal frequency increased to 4000 Hz. The magnitude of suppression was much larger with a noise masker than with a tonal masker, which could be a result of the different number of components in the masker which might serve as a suppressor.
Loudness perception with pulsatile electrical stimulation: The effect of interpulse intervals
Authors: McKay Colette M. , McDermott Hugh J.
Published: July 2002

The effect of interpulse intervals on the perception of loudness of biphasic current pulse trains was investigated in eight adult cochlear implantees at three different stimulus levels encompassing the psychophysical dynamic range. Equal-loudness contours and thresholds were obtained for stimuli in which two biphasic pulses were presented in a fixed repetition period (4 and 20 ms), and also for single-pulse/period stimuli with rates varying between 20 and 750 Hz. All stimuli were of 500-ms duration, and the phase durations of each pulse were 100 μs or less. The results of these experiments were consistent with predictions of a three-stage model of loudness perception, consisting of a peripheral refractory effect function, a sliding central integration time window, and a central equal-loudness decision device. Application of the model to the data allowed the estimation of neural refractory characteristics of the subjects’ remaining peripheral neural population. The average neural spike probability for a 50-Hz stimulus was predicted to be about 0.77, with an associated neural refractory time of 7.3 ms. These predictions did not vary systematically with level, implying that the effect of increasing current level on loudness results more from recruitment of neurons than from any increase in average spike probability.
Comments on “Acoustic dispersion and attenuation in many spherical scatterer systems and the Kramers–Kronig relations” [J. Acoust. Soc. Am. 101, 3299–3305 (1997)]
Authors: Leander Johan L.
Published: July 2002

The aim of this Comment is to suggest some possible improvements and developments of the investigation by Zhen Ye [J. Acoust. Soc. Am. 101, 3299–3305 (1997)]. Particular attention is given to the causality concept and the use of integral theorems.
Across-channel intensity discrimination in the presence of an interferer
Authors: Hill Nicholas I. , Bailey Peter J.
Published: July 2002

Listeners’ thresholds for discriminating changes in the relative intensities of two octave-spaced pure tones were measured in three conditions using a 2AFC procedure. In the baseline condition the tone pair was presented alone, while in the two interference conditions the tone pair was accompanied by four additional tones, with the frequency separation between adjacent components of the resultant six-component complex being one octave. In the interference conditions the flanking components were either gated synchronously with the target pair, or began 200 ms ahead. The level of the flanking components relative to the target was randomized on each presentation. The overall stimulus level was also randomized on each presentation to reduce the effectiveness of within-channel comparisons. Threshold elevations in the synchronous condition relative to the baseline ranged from approximately 5 to 17 decibels. By contrast, in the asynchronous condition only one listener showed significant (although substantially reduced) interference. The results complement previous observations that across-channel intensity comparisons are poorer between components that begin or end at different times, and are qualitatively consistent with the hypothesis that temporal misalignment promotes the perceptual segregation of simultaneous frequency components.
Potential for the presence of additional stop bands in the modal response of regularly ribbed cylinders
Authors: Maidanik G. , Becker K. J.
Published: July 2002

When, in a given frequency band, the magnitude of the line impedance of the ribs approaches and exceeds the line impedance of a moderately damped shell, to which the ribs are attached, a stop band emerges. This stop band need not coincide with any of the usual series of stop bands that are associated with the spacing regularity of the ribs. In this sense, this stop band is dubbed “additional.” The enhancement in the magnitude of the line impedance of the ribs may be caused by a resonance; e.g., if the line impedance of the ribs is commensurate with that of a sprung mass and the loss factor of this dynamic system is low, at resonance, the magnitude of the line impedance of the ribs is relatively high. This resonance enhancement in the line impedance of the ribs may contribute an additional stop band centered about the resonance frequency of the resonant ribs. Examples of additional stop bands in the response of regularly ribbed cylinders are cited and displayed in this paper.
On the possibility of the time-reversal method use in animal echolocation
Authors: Raichel Daniel R.
Published: July 2002

A number of theories have been advanced on the concept of echo evaluation in the auditory systems of bats and cetaceans. K. L. Beuter suggested that bats use neurological processes to evaluate echoes, and Berkowitz and Suga (1989) found different neural mechanisms in two species of bats. Raichel expressed his belief that cetaceans as well as bats are capable of spectral evaluation of signals to obtain information on their surroundings. Palakal and his co-workers developed a cortical model of the neural processing of acoustic patterns entailing temporal pattern recognition (1995). In an application of the phase conjugation method of nonlinear optics, M. Fink developed the acoustic concept of time reversal mirrors in the 1980s and applied it to evaluate materials. Kuperman, Hodgkiss, and Song (1998) demonstrated via experiment that the time-reversal mirror can be used in the ocean to refocus an incident acoustic field back to its origin. Combining the elements of the above cited theories, it is conceivable that cetaceans (and bats) can apply the time-reversal principal to evaluate the reflections of the signals they emit in the course of echolocation.
Two- and three-dimensional heterogeneity in carbonate sediments using resistivity imaging
Authors: Jackson Peter D. , Flint Robert C. , Briggs Kevin B.
Published: July 2002

Improving the characterization of buried inhomogeneities will lead to better models for predicting bottom acoustic backscattering. Sediment volume heterogeneity has been investigated using fine scale electrical resistivity data which is sensitive to porosity and sediment structure, both macro and micro. 3D electrical resistivity experiments are described where a 2D network of resistivity electrodes was used on the surface of freshly collected box cores from the Dry Tortugas, Key West. The resulting 3D resistivity data provides a unique insight into the spatial variability of sediment porosity and structure at the cm scale. Complementary X-radiograph cores provided 2D datasets of resistivity and porosity, at higher resolution. They have been used to establish the porosity-resistivity-microstructure relationships for these carbonate sediments, with microstructure being described in terms of tortuosity. These relationships have been used to extend our interpretation in terms of porosity and tortuosity to the corresponding 3D box core resistivity datasets. Sediment tortuosity has been investigated by numerically modeling the flow of electrical currents through a range of pore morphologies in three dimensions. The results show particular sensitivity to the connectivity of intra-particle porosity, particle shape and the relative sizes of pores and throats.
Validation of a method for educing liner impedance in the presence of grazing flow
Authors: Tracy Maureen B. , Watson Willie R.
Published: July 2002

A method for extracting the normal-incidence acoustic impedance of a test liner installed in the lower wall of a duct carrying a uniform flow was previously reported [W. R. Watson, M. G. Jones, and T. L. Parrott, AIAA paper No. 98-2279 (1998)]. This method has been extended to include the effects of shear flow and has been applied to data obtained for two dissimilar liners in the presence of grazing flow. The normal incidence impedance spectrum of the first liner was known to be flow independent while that of the second liner was expected to be flow dependent. A total pressure survey of the flow-impedance tube was performed to obtain an accurate description of the mean flow field in the vicinity of the liners. Acoustic data was obtained for a frequency range of 0.5–3.0 kHz and flow Mach numbers up to 0.5. Impedance spectra educed without flow for both liners reproduced that obtained experimentally in a normal-incidence impedance tube. As expected, when the grazing flow was turned on, the educed impedance spectra for the first liner showed no sensitivity to the grazing flow while that of the second liner was flow dependent.
Exhaust mixing noise computed from time-accurate simulation of compressible free jet turbulence
Authors: Schein David B. , Meecham William C.
Published: July 2002

A computational fluid dynamics model for free, heated jet flow and resultant far-field sound has been developed which uses large-eddy simulation (LES) and Lighthill’s acoustic analogy. A subgrid scale model for small-scale compressible turbulence is employed incorporating a combination of the popular Smagorinsky model and a deductive model. The model has been tested using published experimental mean flow field and rms fluctuation data [W. R. Quinn and J. Militzer, Phys. Fluids 31(5) (1988)] for a turbulent free square jet. The ultimate objective is to address large Reynolds number, high subsonic (compressible) flow with realistic geometries more representative of aircraft engine exhausts than typically considered using direct numerical simulation (DNS). The far-field sound and directivity is computed using the time-derivative form of Lighthill’s source-integral result formulated in terms of quadrupole sources from the simulated flow field, which is integrated in time and contains the fluctuations set up by the time-varying stress tensor. Simulation for a WR 19-4 turbofan engine exhaust (Re≊2×106 based on exit velocity and diameter) was performed, and propagated jet noise results compared with experimental acoustics data.
Effect of issue conditions and jet nozzle shape on jet noise
Authors: Kouznetsov Vladimir M. , Munin Anatoli G. , Makashov Sergey Yu. , Vlasov Evgeny V.
Published: July 2002

The results of experimental and predicted investigations on aeroacoustic characteristics of jets issuing from ejector noise-suppressor nozzles designed for power plants of supersonic passenger aircraft of the second generation are presented. Different versions of rectangular nozzles with ejector are investigated, the design of which and position relative to the nozzle exit plane vary. Jet noise level reduction by the value of 4 to 5 dB was achieved without substantial variation of thrust characteristics. In the case of jet issue from a rectangular nozzle with the exit section of special form, the discrete noise components at supercritical pressure ratios in the nozzle were completely suppressed. When a multi-element corrugated ejector nozzle was used, jet noise level reduction over a wide frequency range was observed in comparison with the case of jet issue from an annular nozzle of identical exit section area. In the frequency range corresponding to the component of the so-called ‘‘mixing noise,’’ the jet noise level reduction achieved the value of 14 dB. Predicted evaluation of the efficiency of applying a multi-element ejector nozzle on the basis of evaluating the components of ‘‘mixing noise’’ and ‘‘lobe noise’’ was realized. The investigation results for noise of jets issuing from singular corrugated elements showed that jet noise level reduction by the value of 3–4 dB could be achieved at the expense of varying corrugation cross-section shape. [The investigations were partly realized with support of International Scientific-Technical Center (ISTC) according to Project ISTC-TsAGI ♯200-95.]
Dependence of surface wave nonlinearity on propagation direction in crystalline silicon
Authors: Kumon R. E. , Hamilton M. F. , Il’inskii Yu. A. , Zabolotskaya E. A.
Published: July 2002

The nonlinearity matrix elements Rlm (corresponding to generation of harmonic l+m) for a surface wave in a crystal depend on both the plane of propagation and the direction of propagation in that plane [Hamilton et al., Nonlinear Acoustics in Perspective, edited by R. J. Wei (Nanjing U.P., Nanjing, 1996), pp. 64–69]. Propagation at angle θ with respect to the 〈100〉 direction in the (001) plane of crystalline silicon was considered. Because of symmetry it is sufficient to investigate Rlm(θ) for 0°≤θ≤45°. Consider first R11, which corresponds to second-harmonic generation. The sign of R11 indicates whether finite-amplitude effects cause a waveform to steepen forward or backward. R11<0 for 0°≤θ<21° and 32°<θ≤45° is obtained, with R11>0 for 21°<θ<32°. Moreover, it appears that all elements Rlm(θ) have the same sign dependence and zero crossings (θ≂21° and θ≂32°). Numerical simulations reveal that for 0°≤θ<21° and 32°<θ≤45° positive segments of the longitudinal particle velocity waveform steepen backward in space (i.e., opposite what a sound wave does in air), they propagate almost linearly at θ≂21° and θ≂32°, and between these angles they steepen forward. Nonlinearity thus varies far more strongly than small-signal sound speed as a function of propagation direction. [Work supported by ONR.]
Localization of cracks using vibromodulation detection technique
Authors: Sutin Alexander M. , Donskoy Dimitry D.
Published: July 2002

The vibroacoustic modulation technique has been recently introduced as a new tool for nondestructive inspection and evaluation of fatigued, defective, or fractured materials. This technique employs the nonlinear interaction of ultrasound and vibration in the presence of defects. Vibration changes the contact area within a defect effectively modulating an ultrasonic signal passing through this varying contact interface. This paper presents further development of the modulation technique enabling it to determine the location of a defect. The authors have developed and tested various algorithms to find crack location. There are time domain and frequency domain based algorithms. One of the time domain approaches utilizes the correlation between the location of the crack and the arrival time of the modulated portion of the probe ultrasonic signal. This time is determined by the relative distance between locations of the crack and the impact. Another time domain-based approach uses modulation as a ‘‘mark’’ to distinguish the high-frequency tone-burst probe signal reflected from the crack and from all other structural and material inhomogeneities. The frequency domain algorithm analyzes spectral shape which depends on relative position of an impact and a crack. All of these algorithms have been experimentally tested and verified. [Work supported by Gas Research Institute.]
Self-action of the acoustical wave in glass with cracks
Authors: Nazarov Veniamin N. , Soustova Irina A. , Sutin Alexander M.
Published: July 2002

The recently developed nonlinear acoustic method for nondestructive testing uses the modulation of sound by vibrations. However, there are many other nonlinear acoustic effects that could also be used for nondestructive testing. These effects include: amplitude-dependent internal friction, high-amplitude vibration shifting the resonance frequency, generation of higher harmonics, and others. These effects were observed in a glass rod that was fractured by an intensive laser beam, while a similar unfractured glass rod did not exhibit them. The resonance acoustical field in the glass rod was excited on the frequency about 4 kHz and the strain in this field was up to 10−5. Some of the observed effects varied in time, which suggests a change in the crack contact surfaces due to the acoustical field. A theoretical model of acoustic propagation in cracked media to explain the observed nonlinear behaviors is discussed. [This work is supported by the United States Industry Coalition, with the US DOE Contract W-7405-ENG-36, through the University of California.]
Annapolis Laboratory contribution to structureborne noise measurement and analysis
Authors: Herstein Louis A.
Published: July 2002

The Annapolis Laboratory of the Carderock Division of the Naval Surface Weapons Center has continually been in the forefront of the development of instrumentation and standards for the measurement and analysis of the structureborne noise generated by shipboard machinery. This effort included but was not limited to sensor mounting and calibration techniques, equipment mounting fixtures, analysis instrumentation, and criteria for permissible shipboard machinery noise levels. The Laboratory also established the Machinery Acoustic Data Information Center (MADIC), which provided the Navy’s only central source of such information for ship design and operational requirements. One of the results of this effort was MIL-STD-740, the military standard for machinery noise measurement procedures and criteria. An ASA/ANSI standard S2.16-1997, which was based upon MIL-STD-740, has recently been issued.
Fully and partially constrained elastic–viscoelastic–elastic laminates
Authors: Douglas B. E.
Published: July 2002

This paper addresses the history and philosophy of designing constrained layer damping in heavy structures. It follows research pioneered at the Annapolis Laboratory of the Carderock Division of the Naval Surface Warfare Center from the 1960s to the present, emphasizing the various inherent damping mechanisms embedded in elastic–viscoelastic laminates. The basic damping mechanisms embedded in the elastic–viscoelastic–elastic laminates include shear damping, where plane sections remain plane through the cross section of the laminate, compression Voigt damping, where the face layers move out-of-phase to control resonance response of flexural waves, and shear Voigt damping where the face layers are designed to move out of phase manner to convert in-plane mechanical vibratory energy to heat. Closed-form expressions for the complex wave number of these three mechanisms are presented and discussed. The shear damper is found to be useful for light extended structures requiring broadband damping, e.g., fatigue problems in aerospace applications. The compression Voigt and shear Voigt dampers are found useful for heavy structures requiring narrow-band damping, typically a few octaves. The role of constraining layer discontinuity is discussed in terms of nondispersive and dispersive.
The structure of repetition strings in the Switchboard corpus
Authors: Girand Cynthia , Bell Alan , Jurafsky Dan , Fosler-Lussier Eric
Published: July 2002

An investigation of reduction in the ten most frequent English function words in Switchboard, to be presented at ICSLP’98, found that repetition or following silence or filled pause, which were taken as symptoms of planning problems, were strongly associated with longer durations and lack of reduction, extending earlier results for the definite article [J. E. Foxtree and H. H. Clark, Cog. 62, 151–167 (1997)]. As a followup to this study, the structure of unplanned repetition strings is examined more closely. The study is based on an analysis of the lexical transcriptions of the repetitions of words and short phrases from over 100 h of recorded conversations from the Switchboard corpus. Detailed information about the phonetic form and contexts of repetitions a retaken from a phonetically transcribed sample of 4 h of conversation [S. Greenberg et al., ICSLP 96 Proc. (1996)]. Repetitions are overwhelmingly unplanned; are overwhelmingly function words; and are mostly single repetitions of words, although complex strings with multiple repetitions of words, and short phrases combined with silences and filled pauses are not uncommon. The form of repetition strings, including internal and overall durations, are related to variables of rate and context.
Speech recognition in a reverberant environment using matched filter array processing and linguistic-tree maximum likelihood linear regression adaptation
Authors: Raghavan Prabhu , Renomeron Richard J. , Che ChiWei , Chenoukh Samir , Yuk Dong-Suk , Flanagan James L.
Published: July 2002

Performance of automatic speech recognition systems trained on close-talking data suffers when the systems are used in a distant-talking environment due to the mismatch in training and testing conditions. Microphone array sound capture can remove some of the mismatch by removing ambient noise and reverberation, resulting in an approximation to a clean speech signal. However, this often does not improve the performance sufficiently. But, using array signal capture in conjunction with Hidden Markov Model (HMM) adaptation on the clean-speech models can result in high recognition accuracy. This paper describes an experiment in which the output of an eight-element microphone array system using MFA processing is used for speech recognition with LT-MLLR adaptation. The recognition is done in two passes. In the first pass, an HMM trained on clean data is used to recognize the speech. Using the results of this pass, the HMM model is adapted to the environment using the LT-MLLR algorithm. This adapted model is then used to recognize the speech. It is shown that the use of MFA and LT-MLLR results in high-accuracy recognition. [Work supported by DARPA Contract DABT63-93-C-0037.] a)Currently at Raytheon Systems Company, Falls Church, VA.
MRI vocal tract measurements of African American and White American boys
Authors: Morris Richard J. , Fitzsimmons Jeffrey R.
Published: July 2002

The purpose of this project was to use magentic resonance imaging (MRI) procedures to reveal any developmental differences between White American and Black American boys. Four boys completed the task, one 10-year-old and one 14-year-old of each racial group. Each boy was positioned on a gurney inside a General Electric 3 Tesla MRI unit. A neck coil was used to obtain all images using a gradient-echo, spin density weighted sequency with an excitation time no longer than 2 ms and a relaxation no longer than 4.9 ms; the total acquisition time per image was no longer than 327 ms. Images were taken during productions of the vowels /i/, /ɑ/, and /u/ and the words ‘‘bottle,’’ ‘‘pot,’’ ‘‘dot,’’ ‘‘tot,’’ ‘‘got,’’ and ‘‘cot.’’ Software was used to determine the oral, pharyngeal and laryngeal boundaries from the images. These boundaries were used to determine the glottal area, vocal fold length, and vocal fold thickness; the height, depth, width and volume of the pharynx; and the height, length, width and volume of the oral cavity. These data were compared with acoustic and aerodynamic data from the same subjects to provide evidence of any vocal tract differences that might underlie perceived speech differences.
Spaces designed exclusively for pipe organs
Authors: Mahoney Robert
Published: July 2002

Rarely are spaces designed exclusively for the needs of pipe organs; most often other musical instruments or ensembles must be accommodated in the same room the organ occupies and as a result the overall acoustical design goals are not those that would most complement the organ’s sound. Rarer still is the design leadership in such projects entrusted to the acoustician. Two such rarities will be presented: the Krapf Organ Studio at the University of Iowa (a remodeling and consolidation of two existing spaces), and the Bales Recital Hall at the University of Kansas at Lawrence (an entirely new space). The development of design goals and the architectural realization of them are discussed. Measurements of several room acoustical attributes were made during the course of construction of the Bales Recital Hall using a variety of techniques which reveal the influence of the introduction of audience seating and the completed organ.
The making of Spivey Hall
Authors: Pirn Rein
Published: July 2002

Since its opening in the winter of 1991, Spivey Hall on the campus of Clayton College and State University in Morrow, Georgia has gained a fine reputation among both performing artists and concert goers. That reputation acquired a new dimension with the dedication, in the spring of 1992, of the Albert Schweitzer Memorial Organ, which from the very beginning had been the raison d’être for the hall’s design. This paper provides an overview of the acoustical design process, presents the hall in words and pictures, examines the numerical results (RT, EDT, TS, C80, G, LEF, IACC), draws comparisons with other similar halls, and concludes with a brief excerpt from a recording made on the Spivey Hall organ.
Surface pressure fluctuations induced by oscillated spoilers in a flow
Authors: Chang S. , Mongeau L.
Published: July 2002

Recent studies have shown the feasibility of controlling the flow-induced resonance of closed pipes or cavities exposed to a grazing flow using oscillated leading edge spoilers [Kook et al., Proc. 4th AIAA/CEAS Aero. Conf., paper 98-2349, Toulouse (June, 1998)]. Oscillated spoilers can be driven to regulate the phase of the discrete vortices shed near the separation point at the upstream edge of the cavity. Significant reductions in cavity pressure levels were achieved using these actuators, in conjunction with robust feedback control methods and a microphone within the resonant cavity acting as the error sensor. In the present study, the vortex shedding process associated with the actuated spoiler was investigated. Flow visualization was performed to provide a qualitative description of the flow field. The surface pressure downstream of an oscillated spoiler hinged on a flat, rigid plane installed in a wind tunnel was measured for a range of free stream velocities, spoiler angles, oscillation amplitudes, and frequencies. The results were compared with predictions from an analytical model based on vortex sound theory.
Rise profiles of initial shocks in sonic boom waveforms
Authors: Pierce Allan D.
Published: July 2002

The pressure versus time in a sonic boom waveform received at the ground usually begins with a sudden rise in pressure which has a duration of the order of 1 to 10 ms. The explanation of the detailed shape of this portion, termed the rise phase, of the waveform has been a challenging research topic for several decades. It is now well established that there are two dominant causes of the finite duration of this phase: vibrational relaxation of the diatomic molecules in the air and atmospheric turbulence. In the present paper, the author attempts to give an account of some of the theoretical issues that one confronts in the search for a quantitative practicable theory that incorporates these causes into predictive models for the rise phase. An assessment is also given of the simpler theories (those not requiring detailed numerical simulation) that have been proposed in recent years. It is argued that, for many purposes, an acceptable estimate of the dominant features of the rise phase can be made with only a limited knowledge of the state of the atmosphere. [Work supported by NASA-LRC.]
Parametric study of supersonic aircraft shape for reduced boom
Authors: Kovalenko Victor V. , Teperin Leonid L. , Zhilin Yuri L.
Published: July 2002

For future supersonic commercial aircraft it is important to know the strength of their sonic booms and to search for ways to reduce levels. This paper discusses: (1) the method of sonic boom calculation, (2) the effect of aircraft parameters on sonic boom magnitude, and (3) the design of an aircraft shape to reduce sonic boom. The pressure field near an aircraft is calculated using a finite-difference marching procedure in conjunction with a linear-theory panel method. With use of Zhilin’s integral, the near field is transformed to a Whitham F-function, which is the initial data for the wave propagation. The problem of wave propagation in the nonuniform stratified atmosphere is solved by a system of nonlinear equations to obtain the sonic boom signature at the ground. A global parametric study was conducted to include the influence of approximately 16 aircraft parameters, such as dihedral and sweep angle, wing location, canard, etc. Also, for a given wing and fuselage volume distribution, the sonic boom level was minimized by adjusting the wing mean camber surface. This solution was obtained by the inverse aerodynamic method based on linear (panel method) and nonlinear (Euler equation) algorithms.
Inversion of sediment properties from chirp sonar data using an extended Biot–Stoll–Gassmann model
Authors: Turgut Altan , Wolf Stephen N.
Published: July 2002

Recently, chirp sonar subbottom profiling systems have been used extensively for subbottom imaging as well as for sediment impedance profile and attenuation estimation [e.g., LeBlanc et al., J. Acoust. Soc. Am. 91 (1992)]. Typical mid-frequency (1–20 kHz) chirp sonar signals are highly attenuated in the sediment which makes the usage of a proper pulse propagation and attenuation model in the inversion algorithm necessary. An extended Biot–Stoll–Gassmann model is proposed in accordance with the reported sound speeds and attenuation values for different types of sediments. This model was used in a time-domain inversion algorithm for the estimation of sediment geoacoustic properties (density, sound speeds, and attenuation) as well as mechanical properties such as porosity and permeability. Sensitivity analysis indicated that the new model provides a rapid inversion of porosity profile even in the case of noisy one-dimensional reflection data. In this case, along with the attenuation estimation, other parameters are conveniently calculated using the proposed model. Finally, inversion results with the established confidence intervals are presented for the chirp sonar data collected during the SWARM experiment [Apel et al., IEEE J. Ocean. Eng. 22(3) (1997)]. [Work supported by ONR.]
Nondestructive evaluation of textile-reinforced composites based on spacial dependence of ultrasonic scattering
Authors: Johnston Patrick H.
Published: July 2002

The lateral symmetry of the fiber architecture of standard composite laminates, having unidirectional plies stacked in parallel planes, often allows the propagation of a normally incident compressional wave to be described as a one-dimensional problem. Simple transmission measurements of the amplitude and time of flight of pulsed ultrasound become simply related to the average sound velocity and attenuation of the composite. In recent years, composites have been developed using woven, braided, knitted, and stitched textiles. Propagation of ultrasound in these materials can no longer be adequately described by a one-dimensional model. Although simple transmission ultrasonic measurements can still be made, interpretation of the ultrasonic signals becomes ambiguous. It is believed that improved material characterization can be obtained by increasing the number of degrees of freedom in the measurement through the use of multiple element transducer arrays. In order to demonstrate the feasibility of using arrays to better characterize textile based composites, measurements were made of the angular variation of ultrasonic scattering from several composites. The incident transducer was aligned normal to the surface of the specimens, while a second transducer was used to measure the scattering as a function of azimuthal angle at various nonzero polar angles.
Quantitative flaw reconstruction from ultrasonic surface wave fields measured by laser interferometry
Authors: Mast T. Douglas , Gordon Grant A.
Published: July 2002

A quantitative imaging method for ultrasonic nondestructive testing of structures is presented. The method employs two-dimensional surface-vibration data that is obtained by laser interferometry methods such as holography and digital phase-stepping shearography. In this method, a surface wave field generated by a narrow-band contacting or noncontacting ultrasonic transducer is Fourier transformed to obtain a spatial-frequency domain representation of the wave field. The appropriate Green’s function is then deconvolved from the wave field to obtain quantitative images of effective scattering sources. Since scattering strength is directly proportional to the local contrast of the structure, these images provide a direct map of internal flaws in structures such as plates and shells. The method is valid for strongly scattering inhomogeneities, and can employ scattered evanescent waves to obtain resolution of flaws much smaller than a wavelength. Simulated and experimental results illustrate the efficacy and quality of the imaging method.
How well does natural motion induce auditory motion aftereffects?
Authors: Neelon Michael F. , Jenison Rick L.
Published: July 2002

There is evidence that a repeatedly traversing sound source induces motion aftereffects in listeners [D. W. Grantham, Percept. Psychophys. 45, 129–136 (1989)]. Other work has found aftereffects for acoustic attributes often involved in motion, e.g., for level or frequency changes [Reinhardt–Rutland, Percept. Psychophys. 28, 569–571 (1980); Shu et al., Nature 364, 721–723 (1993)]. Few studies, however, have investigated adaptation in the presence of more ecologically valid motion. Normally, stimuli in adaptation paradigms include changes in spectral cues and interaural differences but not the changes in amplitude or frequency that occur with motion under more natural spatial trajectories, e.g., linear approach. The questions arise whether such aftereffects are due to fatiguing neurons mostly sensitive to arbitrary interaural modulations, or are units truly responsive to lawful, natural motion? If integrated motion detectors exist, then including amplitude and frequency changes in adapting stimuli should enhance aftereffects. Subjects will be adapted to three types of stimuli: those with interaural changes only, with amplitude and frequency changes only, or with interaural, amplitude and frequency changes following lawful motion. Greater magnitude aftereffects for latter stimuli or aftereffects induced by middle stimuli may reveal which acoustic attributes hypothesized motion detectors are responsive to. [Work supported by NSF.]
Interhemispheric transfer time of audiomotor information
Authors: Bolia Robert S. , Ericson Mark A. , Simpson Brian D.
Published: July 2002

Since the crossed–uncrossed difference technique was first described by Poffenberger [Arch. Psychol. 23, 1–73 (1912)], it has been used numerous times to measure interhemispheric transfer time (IHTT) of visuomotor information via the commissural system [see Marzi, Bisiacchi, and Nicoletti, Neuropsychologia 29, 1163–1177 (1991), for a review]. In spite of its widespread use by vision researchers, this technique has never been used to measure IHTT of audiomotor information. In the present study, audiologically normal dextral listeners made a simple reaction time response to brief spatialized bursts of broadband noise presented dichotically over insert earphones. For each listener, one block of 120 trials was completed with each hand. Half of the stimuli in each of the response conditions (right/left hand) were presented in the right hemifield, the remaining half in the left hemifield. Crossed–uncrossed differences were computed for each listener. Results will be discussed in terms of IHTT for audiomotor information and the possibility of cerebral lateralization of auditory localization processing.
Effect of audiometric test room noise on monaural and binaural thresholds
Authors: Tufts Jennifer B. , Frank Tom
Published: July 2002

This study determined if the maximum permissible ambient noise levels (MPANLs) for audiometry specified in the revision of ANSI S3.1-199x provided the same amount of threshold shift for monaural and binaural listening. Sound-field monaural and binaural warble-tone thresholds (125–8000 Hz) were obtained on 24 normal-hearing subjects in quiet (ambient) and in two background noise conditions. One noise condition approximated the ANSI S3.1-199x ears not covered MPANLs (ANSI noise). The other noise condition was 20 dB higher than the ANSI MPANLs (ANSI noise + 20). Monaural thresholds were about 2 dB higher than binaural thresholds in quiet and in each noise condition. The difference between the monaural minus the binaural threshold shifts in each noise condition (ANSI noise + 20 minus ambient; ANSI noise minus ambient) averaged over frequency was typically less than 1 dB. Thus the MPANLs in the revision of ANSI S3.1-199x are appropriate for both monaural and binaural testing.