bluuebunny/crossref_metadata_2025 huggingface dataset:
Low-frequency acoustic stimulation of fluid flow in porous media
Authors: Roberts Peter M. , Sharma Arvind
Published: July 2002

Historical Russian and U.S. research has indicated that acoustic or elastic (seismic) waves transmitted into oil reservoirs at frequencies of 1–500 Hz can increase oil production rates. Results from prior field tests on reservoir formations and laboratory experiments on porous rock samples have been largely inconclusive. The underlying physical mechanisms are still speculative. Comprehensive experimental laboratory and theoretical data on the interactions between acoustic waves and fluid flow in porous media are required before the phenomenon can be exploited reliably for enhanced oil recovery or other applications such as groundwater remediation. A specialized laboratory facility was constructed to characterize effects that low-frequency stress oscillations have on permeability and two-phase fluid flow in cylindrical rock and sand samples. Applied mechanical axial stress, axial and radial strains, permeability changes, fluid production rates, and dynamic elastic moduli are all measured during excitation of the samples. Positive results were observed for enhanced permeability, mobilization of trapped immiscible fluid phases, and increased production rates for sandstone-brine-decane and sand-water-trichloroethylene systems. These results will be presented along with discussions of possible physical mechanisms involved. [Work supported by the U.S. Department of Energy, Office of Fossil Energy.]
Wind induced infrasound in the atmosphere
Authors: Xie Jin Lai , Xie Zhao Hua
Published: July 2002

Characteristics of atmosphere infrasound noise field have been studied by measuring and analyzing the infrasound noise field in the atmosphere. A set of space correlation radii of noise corresponding to wind speed 4 m/s has been obtained, which can be taken as the tentative basis for an acoustical array design. At the same time, the wind speed-pressure relation curves have been measured and calculated, and the antijamming ability of the array receiving infrasonic signals and noise-reducing tube is obtained. The following conclusions can be obtained from the present calculations, waveform diagrams, and the field measurements: (1) The spatial correlation radii of the noise caused by the wind are small. (2) The measured curves for wind noise are in accordance with Bernoulli theorem basically. (3) The correlation detection is advantageously available for antinoise. (4) The different averaging duration of the wind noise will cause different results. (5) The main source of natural noise background on ground is the aerodynamic noise produced by local surface wind. The main period lies within 1 to 100 s.
Adaptation to a two-component amplitude modulator
Authors: Iwasawa Hideki , Kashino Makio
Published: July 2002

Threshold shifts of amplitude modulation (AM) detection caused by adaptation to single- and two-component amplitude modulators were determined. The single-component modulator was sinusoid at either 4, 17, or 21 Hz. The two-component modulator was a complex of sinusoids at 17 and 21 Hz. The carrier was sinusoid at 1000 Hz for both adapting and test tones. Five adults with normal hearing participated in the 6-day experiment. Adaptation to modulators elevated thresholds of AM detection of the same and nearby frequencies relative to the unmodulated-adaptor or no-adapting conditions. In contrast to the findings in modulation detection interference (MDI), where the low-frequency beat of a masker with a two-component modulator interfered with detection of AM at the beat frequency [S. Sheft and W. A. Yost, J. Acoust. Soc. Am. 102, 1106–1112 (1997)], the two-component amplitude modulator did not affect the threshold for detecting AM at the beat frequency. The present results suggest that envelopes are not detected as such, but resolved into components, and that the mechanism responsible for AM adaptation is earlier in processing level than that involved in MDI.
Fundamental frequency discrimination: Influence of lateralized temporal fringes
Authors: Gockel Hedwig , Carlyon Robert P. , Micheyl Christophe
Published: July 2002

Fundamental frequency (F0) discrimination can be impaired substantially by the presence of another complex (the ‘‘fringe’’) immediately before and after the target complex. This has been attributed to listeners over-integrating information about the fringe F0 when estimating the target F0. It has been shown [C. Micheyl and R. P. Carlyon, J. Acoust. Soc. Am. (in press)] that for the impairment to occur (i) target and fringes have to be in the same frequency region; (ii) if all harmonics of target and fringes are unresolved then they may differ in F0; otherwise, they have to be similar. The present experiments investigated the effect of lateralized fringes. In a 2I-2AFC adaptive procedure, difference limens for F0 for a 100-ms harmonic target complex were measured in the presence and absence of 200-ms harmonic fringes. The nominal F0 was 88 or 250 Hz. Stimuli were bandpass-filtered between 125 and 625, 1375 and 1875, or 3900 and 5400 Hz. The target was presented monaurally, while the fringes were monaural (ipsilateral or contralateral) or binaural (diotic or dichotic, lateralized by ILD or ITD). Results showed reduced effects of fringes localized away from the target, the exact size depending on the resolvability of the components and their specific lateralization. [Work supported by Wellcome Trust.]
Adaptive psychophysics based on unforced-choice tasks
Authors: Kaernbach Christian
Published: July 2002

Perceptual thresholds are usually measured by means of adaptive staircase procedures. The latter are commonly combined with forced-choice tasks in order to avoid problems arising from unstable criteria in yes/no tasks. The present study suggests the use of ‘‘unforced-choice’’ tasks, when the observer is given an additional response alternative, ‘‘don’t know.’’ Simulations and experimental data are presented which demonstrate that if combined with an appropriate adaptive rule, the unforced-choice paradigm can be at least as efficient as forced-choice tasks, if not superior.
Do ears really just perform frequency analysis of crackle sound?
Authors: Blumschein Eckard
Published: July 2002

Experience concerning measurement and interpretation of a special crackle sound which relates to the quality of so-called short arc welding is summarized. There are salient elements in it, which sound different when time is reversed. Other observations also gave rise to put into question the adequacy of traditional, purely spectral processing of acoustical signals. Further evidence has been collected in order to substantiate general needs for a better understanding of how audition might really work, and to justify the search for an approach that could overcome the well-known imperfections of spectrograms. Considerations start with interpretation of data given on response of basilar membrane to clicks by Recio et al. (1998) and on branched, more apical recorded click latencies in Cai’s (1992) thesis. Gammachirp-like behavior of basilar membrane has been considered a superposition of coupled oscillations. The branched latencies were found to fit a conjectured exact relationship to 1/CF surprisingly well. It does not result from the velocity of the traveling wave, but the way around; the latter is merely an epiphenomenon. These findings back an idea that latencies provide an accurate second coding, in addition to place. So, the cochlea itself may act as a delay line, being requisite for autocorrelation-based models of temporal perception.
Scaling regimes in incoherent surface-reflected and in-sediment sound fields
Authors: Smith Eric , Richardson Michael D. , Wood Warren T. , Jans Wolfgang
Published: July 2002

A suite of collocated measurements of broadband in-sediment acoustic propagation and surface reflection was made at nine sites on the Florida shelf and in the Gulf of Mexico, between 16 August and 6 September 1998. Closely spaced in-sediment transmission measurements, and populations of narrow-beam echo soundings, provided ensembles from which mean and incoherent components of propagating and reflected sound fields were derived. The two components contain mutually independent information about the effective bulk properties and heterogeneity of the medium. Attenuation of the direct arrival through the sediment depends on both intrinsic absorption and scattering from heterogeneities. Temporal decay of the incoherent ‘‘coda’’ at a point, not described by homogeneous effective-medium theory, requires scattering to maintain sound energy in a region. Incoherent coda in the surface reflection can be generated either from multiple scattering near the surface, or random reflection within the sediment bulk. Scaling regimes of both kinds of attenuation will be demonstrated and compared, between in-sediment propagation and surface reflection, and among different sites. As a control, scaling of the coda decay constant will also be compared to results of reflection from sand in an indoor tank, from which stratification and surface roughness were removed. [Work supported by ONR.]
Categorical assessments on fluctuation strength of synthesized sounds
Authors: Raubold Imke , Weber Reinhard
Published: July 2002

Results on category scaled fluctuation strength of different kinds of synthesized signals are presented. Fluctuation can become a major aspect of sound quality, and the intent of the study was to investigate the relationship between ratio-scaled data in literature [e.g., Zwicker and Fastl, Psychoacoustics (Springer-Verlag, New York, 1991)] and categorical judgments. Signals used comprise AM or FM tones with different carrier frequencies (0.25, 0.5, 1, 2, 4, 8 kHz) as well as modulated noises. Modulation frequencies vary from 0.25 to 32 Hz in octave steps. The whole set of 66 stimuli each lasting for 6 s was divided into three sequences presented over headphones in a sound-proof cabin. As in previous roughness assessments [Daniel and Weber, Acustica 83, 113–123 (1997)] judgments were made using an ‘‘analog’’ category scale consisting of five categories (not -, a little -, medium -, rather -, and very fluctuating) which are combined with a continuous scale to overcome limited resolution of the categories. It turns out that the concept of fluctuation is interpreted differently by subjects, especially by ‘‘naives’’ and already trained ‘‘experts.’’ The consequences for the different kinds of noises will be discussed as well as the relationship to ratio-scaled data.
Anisotropy and sound propagation in glass wool
Authors: Tarnow Viggo
Published: July 2002

Sound propagation in glass wool is studied theoretically and experimentally. Theoretical computation of attenuation and phase velocity for plane, harmonic waves will be presented. Glass wool is a highly anisotropic material, and sound waves propagating in different directions in the material will be considered. The computations are based on the geometry of the glass wool that is decribed by the density of fibers and their diameters. The air drags viscously on the fibers, and movements of the fiber skeleton are important at low frequencies. Propagation of elastic waves in the skeleton is computed by regarding it as a continuous medium described by its elastic moduli and mass density. The computed attenuation of sound waves, for frequencies 50–5000 Hz, will be compared with experimental results for glass wool with fiber diameters of 6.8 micrometers, mass density of 15 and 30 kg/m3, and elastic moduli of 2000 and 16 000 Pa (sound wave vector perpendicular to fibers).
The action programme of UIC and CER (Community of European Railways) ‘‘abatement of railway noise emissions from goods trains’’
Authors: Hübner Peter
Published: July 2002

Although rail transport has a low environmental impact overall, noise from goods trains remains a major problem. Research has identified that wheel roughness is the critical factor and that composite materials will deliver adequate braking with less damage to the wheel surface than existing iron brake blocks. Accordingly the UIC/CER has made a formal commitment to fit composite blocks to existing wagons, as well as to all new wagons. Existing wheels cannot cope with the thermal stress from composite blocks. Fitting new wheels only when the old are worn out will be cost neutral, but will take 15–20 years. Premature wheel replacement will involve additional cost, but will deliver the benefits in 5 years. This can be achieved with financial assistance from E.U. member-states, who will thereby avoid unnecessary outlay on noise barriers. At the same time proposals for a E.U. noise creation standard should reflect the performance achieved by the modified wagons. The railways propose a voluntary environmental agreement with the E.U.
Oscillations in harmonics generated by the interaction of acoustic beams
Authors: Cahill Mark D. , Baker Andrew C.
Published: July 2002

A numerical model of nonlinear propagation is used to investigate two cases of monochromatic ultrasonic beams interacting at small angles in a nonlinear medium. Two finite Young’s slits are seen to produce fringes at harmonic frequencies of the source in places where the source frequency is absent, which can be seen as a combination of harmonic generation near the source, and in the beam. Two intersecting beams with shaded edges are seen to produce similar fringes in the near field, with an oscillatory structure. Algebraic solutions to a simplified model, using the weak-field Khokhlov–Zabolotskaya equation, are invoked to illustrate the origin of the oscillations, and of the far-field directivity, providing an alternative view of the fringes due to Young’s slits. It is seen that two weakly interacting beams can produce fringes of second harmonic where the source frequency has low amplitude, if the beams coincide at the point of observation, or if a boundary condition is imposed on the second harmonic where the beams coincide.
Theory of the backscattering of sound by phase-matched nonlinear interaction
Authors: Kouznetsov Dmitrii , Garcı́a-Valenzuela Augusto
Published: July 2002

The nonlinear interaction of noncollinear acoustical waves is considered. Conditions of the resonant backscattering of one wave from the lattice produced by the other two are formulated in analogy with the four-wave mixing known in optics. The efficiency of the phase-matched interaction of acoustical waves is calculated in the resonant approximation for a gas media. Such approximation is constructed on the basis of the expansion of the sound equations preserving up to cubic terms. The amplitude of the backscattered wave is expressed as the product of the efficiency, the amplitudes of three waves, the wave number of the backscattered wave, and the size of the region of interaction. Such backscattering is proposed as an acoustical remote probe. The distance to the interaction region and the amplitude of initial waves are limited by nonlinear degradation of waves due to the second-order nonlinearity. For acoustical waves with wave number 10 m−1, sources of size 1 m, and about 100 m to the interaction region, the amplitude of the backscattered wave can be about 10−10 of the atmospheric pressure. At the detection with a signal-to-noise ratio about of 10, the resolution of such method on the wind velocity may be about 1 m/s.
Subarctic frontal effects on long-range acoustic propagation in the North Pacific Ocean
Authors: Shang E. C. , Wang Y. Y.
Published: July 2002

Acoustic propagation along the Hawaiian–Aleutian path at low frequency (65 Hz) for the acoustic thermometry of ocean climate (ATOC) has been simulated using the implicit finite difference parabolic equation (IFD-PE). This simulation is based upon the Semtner–Chervin model with one-half-degree resolution. The adiabaticity has been assessed, and it was found that significant mode coupling takes place at the sub-arctic front area (44.8 ° N). Due to the range-dependent double channel, two characteristic ranges were identified in this area: (i) the modal degeneration range RmD and (ii) the modal scattering range RmS. At range RmD, mode m and mode n (usually, n=m+1) are degenerated, the modal wave numbers of mode m and mode n become equal, and mode n then takes the shape of mode m. Therefore, there is no real repopulation (modal scattering), but a modal name change takes place at this range. The modal name change can cause a miscalculation of the adiabatic travel time. At range RmS, however, real repopulation does take place. Numerical simulations illustrate that RmD and RmS are separated by about 10 km at lower modes (m<5) and are merged at higher modes.
Response to “Comments on ‘Broadband spectra of seismic survey air-gun emissions with reference to dolphin auditory thresholds’ ” [J. Acoust. Soc. Am. 105, 2047–2048 (1999)]
Authors: Goold John C. , Fish Peter J.
Published: July 2002

In a prior paper, “Broadband spectra of seismic survey air-gun emissions with reference to dolphin auditory thresholds” [J. Acoust. Soc. Am. 103, 2177–2184 (1998)] a comparison was drawn between the estimation of sound levels at a distance which unconstrained dolphins would appear to maintain from a seismic air-gun source and the sound threshold at which captive dolphins displayed behavioral changes as reported by [Tech. Rpt. 1751, NCCOSC RDTE (1997)]. This prompted comments in the letter above on the validity of the conclusions of the prior paper. In this rebuttal, it is pointed out that uncertainties in the sound levels estimated in the prior paper arising from uncertainties in distance estimation, sound-propagation model, frequency weighting, and allowance for pulse duration are most unlikely to account for the very large difference of 48 dB between Goold and Fish’s results and Ridgway’s. The differences in criteria for deciding the threshold—behavior suggesting distress in captive dolphins (Ridgway et al.) and the assumption that dolphins swim to a distance at which the sound is tolerated (Goold and Fish), is the most likely explanation for the difference in the published figures.
The role of scale structure in scattering from random rough surfaces
Authors: Lupien Vincent
Published: July 2002

Scale structure is defined as the stochastic spatial arrangement of an interface’s component features at various scales. The principal contribution of this study is to demonstrate that scale structure is a useful and acoustically meaningful concept for characterizing a stochastic scattering surface’s roughness. The information contained in scale structure about an interface’s roughness supplements that contained in the power spectral density (PSD). This fact is demonstrated by observing that the scale structure of different stochastic surface models with a common power spectral density of the power-law type varies from feature-like at one extreme to fractal, non-feature-like at the other. To investigate the impact of scale structure in scattering, the ensemble scattering statistics of each surface model are computed using an exact Monte Carlo integral equation technique and 50 realizations each. It is found that both the bistatic scattering strength and the time-domain statistics of scatter are significantly affected by differences in scale structure given a constant PSD. This result is relevant in any scenario involving the scattering of waves from natural interfaces because while landforms usually have a power-law PSD, they exhibit a wide range of scale strucutres. To contrast the roles played by scale structure and the PSD in scattering, surface models with vastly different PSDs but similar scale structure are compared. It is found that while the PSD’s role is preeminent for average scattering strength in the back quadrant, scale structure establishes the presence of a forward scatter lobe and the degree of event-like (non-Rayleigh) behavior in time-domain scatter; both are enhanced in feature-like surfaces. As a new way of looking at roughness, scale structure suggests many possibilities for future research, some of which are presented herein.
Resonant oscillation of a liquid metal column driven by electromagnetic Lorentz force sources
Authors: Makarov Sergey , Ludwig Reinhold , Apelian Diran
Published: July 2002

In this paper, a theoretical study is conducted in order to establish the feasibility of a liquid metal acoustic resonator (liquid gallium or liquid aluminum) for high-amplitude acoustic oscillations. The fundamental resonant frequency typically lies between 5 and 40 kHz. The oscillations are induced by an alternating Lorentz force density applied directly to the liquid metal volume. Depending on the boundary conditions, two different resonator types (open–closed and open–open) are theoretically investigated. The analysis incorporates the effects of impedance termination, volume absorption, wall friction, acoustic radiation from the open end, and nonlinear inflow–outflow losses. The actual elasticity of the container, either a ceramic or quartz tube, and the coupled solid–liquid interactions are taken into consideration. Based on this investigation, theoretical predictions are conducted for the quality factor and the pressure level for the liquid metal resonator under various geometric and boundary conditions. They indicate that resonant amplitudes of 10–20 atm can be achieved using commercially available high-current audio amplifiers.
Separation of an acoustic signal from noise via the use of point pressure and velocity measurements
Authors: Stepanishen Peter R.
Published: July 2002

The separation of an acoustic plane wave signal from noise via the use of pressure and velocity measurements at a point is investigated using a time domain and Fourier transform approach. The noise is assumed to originate from a compact source at a known location. A time domain analysis of the separation method for the deterministic signal problem is first presented. A spectral analysis which provides additional insight into the method is then presented. An analysis of the sensitivity of the signal separation method to processor errors including quantization errors and extraneous uncorrelated sensor noise is also presented. Numerical results for some simple examples illustrate the use of a digital signal processor for separating signal from narrow-band and broadband noise. The sensitivity of the signal separation method to processor errors including numerical differentiation and quantization errors is simply illustrated via the examples. In addition, the sensitivity of the separation method to the noise source/sensor separation distance is also presented.
Parameter uncertainty analysis on acoustic response in fluid filled poroelastic media
Authors: Mu Yongke , Badiey Mohsen , Cheng Alexander H.-D.
Published: July 2002

This paper examines the effect of input parameter uncertainty in the prediction of acoustic response in ocean sediment. Due to the relatively large number of physical parameters in the model, and the difficulty of their direct measurement in the ocean environment, uncertainty in the predicted acoustic response is expected. Utilizing a second order Taylor series expansion, this paper demonstrates a methodology for estimating the output uncertainty in terms of statistical moments from the input uncertainty. The methodology is then tied to a practical procedure that uses engineering measurements and empirical relations to determine parameters such as shear modulus, bulk modulus, and permeability, from porosity. A related issue of pore size distribution and its effect on acoustic response is also investigated.
Surface backscattering statistics for observations conducted near Kiel, Germany
Authors: Ruppel Timothy H. , Feuillade Christopher , Stanic Stephen J.
Published: July 2002

In May 1993, an experiment was performed off the coast of Kiel, Germany to study the temporal variability of backscattering from the ocean boundaries. In the sea-surface backscattering component of the experiment, two dual-mode acoustic transducers were used to ensonify the surface with 1 or 3 ms pings at 20–90 kHz and incident angles of 65.1°−80.9° from normal. The transducers also recorded the backscattered sound. Analysis of the overall returns shows that they vary significantly from ping to ping, such that the distribution of backscattered energy appears nearly Gaussian. However, close comparison of all the signals from a given run indicates the presence of strong salient patterns in some cases, which suggest scattering from individual features (presumed to be wave crests) which move through the beam pattern from ping to ping. The statistics of the backscattered signal from these features, and their relation to the overall backscattered energy statistics, is the topic of this paper. [This work was funded by the Office of Naval Research.]
Parabolic equation techniques for diffraction and scattering problems
Authors: Mills Michael J. , Collins Michael D.
Published: July 2002

The parabolic equation method has proven to be useful for solving single-scattering problems [M. D. Collins and R. B. Evans, J. Acoust. Soc. Am. 91, 1357–1368 (1992)]. Parabolic equation techniques for more difficult scattering problems will be presented. An approach involving parabolic approximations for range derivatives and an iteration scheme for the reflected and transmitted fields has been developed for solving problems such as the Sommerfeld diffraction problem and scattering from baffled membranes [Kriegsmann et al., J. Acoust. Soc. Am. 75, 685–694 (1984)]. This approach has been generalized to include multiple scattering events, with applications such as scattering from compact objects. The parabolic equation techniques will be described and illustrated with examples. [Work supported by ONR.]
Driving the virtual orchestra with a conductor gesture interpreter
Authors: Bianchi Frederick W. , Campbell Richard H.
Published: July 2002

The interactive multichannel computer music system known as the ‘‘virtual orchestra’’ (VO) has been used several times in professional opera and theater as an alternative to a live pit orchestra. In each case, the VO has been operated by a ‘‘tapper’’ who follows the conductor and operates the computer which controls the VO. Recent research in noncontact, video-based conductor gesture interpretation has shown interesting possibilities in tempo and limited musical dynamics management when the gesture interpreter is directly connected to the VO controller. Two different approaches to conductor gesture detection will be discussed and the virtual orchestra will be demonstrated.
Intelligent computer accompaniment systems
Authors: Dannenberg Roger B.
Published: July 2002

Because real-time computer music systems are automated, portable, and affordable, they are finding increasing application in live performance. Unfortunately, most computer music systems offer little more than a tape recorder in terms of their abilities to interact with live musicians. Computer accompaniment is designed to go beyond this ‘‘tape recorder’’ model of human–computer interaction. Computer accompaniment is a process in which a computer ‘‘listens’’ to a live musician, follows along in a score, and synchronizes an accompaniment score with the live player. Computer systems can reliably accompany a live musician in spite of tempo changes and wrong notes. Many variations of computer accompaniment have been developed. The original work assumed only one live musician playing a monophonic wind instrument such as a trumpet or flute. One variation is to follow the polyphonic performance of a keyboardist by sensing the motion of keys. In ensemble accompaniment, the task is to accompany multiple players. In addition to playing wrong notes, individual players might drop out or become lost, so there are interesting new issues to be dealt with. This work addresses practical problems of integrating computer-based performers with live performers.
Focus-directed processing of acoustic holography images
Authors: Yin Ruming , Broschat Shira L. , Flynn Patrick J.
Published: July 2002

Acoustic holography is a transmission mode imaging technique which was first proposed in the 1970s. As with optical holography, an image is obtained using coherent interference of the transmitted acoustic signal with a reference signal. The interference pattern is illuminated with a laser, and the resulting image is digitized. However, since image reconstruction is performed optically, acoustic holography introduces a focusing problem characteristic of optical systems. Ideally, an image is focused on tissues at a given depth along the optical axis—that is, in one planar slice of the object. In practice, the image is focused over a range of depths so that objects at different depths are blurred but still visible. In this paper, we consider several postprocessing algorithms developed to improve images obtained using an acoustic holography system. First, a focus measure technique is used to determine when the object of interest is best focused. Second, a technique called depth from focus is used to determine the depth of an object. Third, a technique is developed to increase the ‘‘in focus’’ interval, or focusing range. These techniques will be discussed and imaging results will be presented. [Work supported by the National Science Foundation and the Carl M. Hansen Foundation.]
Classical measurements of sound
Authors: Hixson Elmer L.
Published: July 2002

From the 1500s the study of sound involved acoustics and vibrations. Early theoreticians tried to experimentally justify their analytical models. Many vibrating devices were available to generate acoustic waves but few means were available to quantify these sources and sound propagation. The human ear was the only means of amplitude measurement and spectral analysis. The development of electrical and electromechanical technology allowed great advancements in the measurement of sound. Bell’s telephone transmitter/receiver and Flemming’s valve brought great strides in quantifying sound. The capacitor microphone brought high accuracy. The advent of the oscilloscope and electrical filters provided analysis of complex sounds. This level of technology served the field well until the advent of the computer age.
Laboratory experiments as demos and projects in the underwater acoustics and sonar course
Authors: Simmons Elizabeth L. , Korman Murray S.
Published: July 2002

Underwater Acoustics and Sonar (SP411) is a 3-h course that is typically offered to Midshipmen in their senior year. General science majors take the course in the fall while the oceanography majors enroll in the spring. A sprinkling of physics, electrical engineers, ocean engineers, and systems majors also populate the course (totaling ∼110 students/yr). Since this course is offered without a lab, the ‘‘in-class’’ experience has been enhanced with the development (over many years) of our demo carts which surround the classroom. Although Friday is our major ‘‘demo day,’’ demos are performed throughout the week. They motivate the students’ ‘‘out-of-class’’ experimental projects. Demos include: (a) waves on slinkies; (b) Fourier analysis of tones in noise, homemade musical instruments; (c) harmonic synthesis; (d) receiver operating characteristics from processed signals in noise; (e) two-element and loudspeaker beam patterns; (f) sound speed versus temperature in water; (g) target strength versus angle of a model sub; (h) Ref. coef. from an Al/water interface; (i) PC-IMAT (interactive multisensor analysis training) simulations of array steering, ray tracing, active sonar, propagation loss; and (j) FM detection and Doppler effects. Students get involved with the measurements, have fun, and their understanding of underwater sound is greatly enhanced.
The acoustic interferometer as a teaching laboratory experiment
Authors: Gabrielson Thomas B.
Published: July 2002

Interferometry is a popular subject for teaching-laboratory experiments in optics. Furthermore, some important classes of acoustic and vibration sensors rely on optical interferometry. Consequently, the fundamentals of interferometry and the interpretation of the resulting signals are important concepts even outside the field of optics. Unfortunately, procurement, alignment, and maintenance of optical interferometers can be prohibitively expensive for a program that does not specialize in optics. For institutions lacking a substantial infrastructure in free-air or fiber optics, the acoustical interferometer is an attractive alternative. Most of the issues associated with optical systems can be incorporated into straightforward laboratory exercises. The components for a 40-kHz acoustical system are inexpensive and readily available. The alignment is greatly simplified by the much longer wavelength and the function of the components is more intuitive. Moreover, absolute displacement calibration can be done with conventional micrometer translation stages; the effects of different bias points can be investigated; and the characteristics of large-signal behavior in interferometers can be studied. For advanced experiments, a heterodyne interferometer can be constructed along with a simple demodulator. [Work supported by the Graduate Program in Acoustics at Penn State.]
Acoustic signatures of a fracture during air injection
Authors: Nihei Kurt T. , Peterson John E. , Myer Larry R. , Majer Ernest L.
Published: July 2002

This study examines the acoustic signatures of transmitted, reflected, and guided waves during air injection into a single, natural, water-saturated fracture in limestone. The presence and location of the fracture were established in a series of geologic, hydrologic, and seismic studies (Queen and Rizer, 1990; Datta-Gupta et al., 1994; Majer et al., 1997) that ultimately led to its verification in core obtained from a slanted well. This work describes the results of a follow-up high frequency (1 to 10 kHz) crosswell survey that was designed to illuminate the fracture by air injection into the fracture. Zero-offset P-wave crosswell transmission and reflection measurements conducted during air injection showed a large decrease in the amplitude of the transmitted wave (approximately 10 times reduction at 3 kHz), and a smaller increase in the amplitude of the reflected wave (approximately 1.5 to 5 times increase at 3 kHz). Measurements of the P-wave and an interface wave propagating along the fracture also show a small increase in amplitude during air injection. Analyses of these measurements using numerical boundary element and finite-difference simulations and the importance of including fracture stiffness heterogeneity arising from irregular distributions of air inside the fracture will be presented.
Seasonal variability in the atmosphere and its effect on infrasonic propagation
Authors: Norris David E. , Gibson Robert
Published: July 2002

Infrasonic waves can propagate thousands of kilometers in range and sample regions of the atmosphere from the ground up to and including the thermosphere. In this study, seasonal changes in the atmosphere and their effect on infrasonic propagation are characterized. The NASA/NRL empirically based models HWM-93 (for winds) and MSIS-90 (for temperature) are used. Three-dimensional ray traces are computed through the modeled atmosphere for several representative scenarios. Seasonal trends in both ray arrival times and ray azimuth bias are computed, and limited comparisons with data are made where possible. [Sponsored by Defense Threat Reduction Agency, Contract No. DSWA01-97-C-0160.]
Numerical solution of a second-moment parabolic equation for sound propagation in a random medium
Authors: Wilson D. Keith , Ostashev Vladimir E.
Published: July 2002

A parabolic equation for the second-moment of the acoustic pressure field in a refractive medium with random fluctuations is derived using the Markov approxiation. The PE is then discretized and written as a matrix equation for the purpose of numerical solution. The matrix equation involves the product of an N2z×N2z tridiagonal matrix with ‘‘fringes’’ times the N2z×1 second-moment vector, where Nz is the number of points in the vertical grid. (The numerical formulation of the usual PE for the acoustic pressure involves an Nz×Nz pure tridiagonal matrix.) Direct solution of this extremely large linear system is prohibitive. A pair of alternative strategies are therefore devised. One involves Cholesky factorization of the second-moment matrix. The other is based on iterative solution of the second-moment equation, with the coherent field used to start the iterations. Both of these methods are applied successfully to propagation in an upwardly refracting atmosphere, although solution of the second-moment PE is still very computationally intensive. [Work supported in part by the U.S. Army Research Office under Contract No. DAAG55-98-1-0463, and NRC-ETL Research Associateship.]
Factors accounting for performance in a frequency-sample-discrimination task with distracters
Authors: Neff Donna L. , Odgaard Eric C. , Jesteadt Walt , Dai Huanping
Published: July 2002

This paper presents results of fitting several linear models, including the CoRE model of Lutfi [R. A. Lutfi and K. A. Doherty, J. Acoust. Soc. Am. 96, 3443–3450 (1994)] to data from a study of the interaction of target and distracter tones in a sample-discrimination task. In this 2IFC task, ten listeners judged which of two pairs of target tones were drawn from the higher of two overlapping frequency distributions. After training with targets alone, two distracter tones were presented simultaneously with the target tones, with each distracter placed in a frequency region remote from the target region. The important variables were the frequency regions and degree of frequency variability of targets versus distracters. Main features of the data included a large range of individual differences, a dominance of the effects of lower-frequency context tones over the higher-frequency context tones in many conditions, and differences in performance in the baseline, no-context conditions. When stimulus variability, perceptual weights across frequency, and performance in the no-context conditions are included as factors in the analysis, both mean and individual performance can be described reasonably well. [Work supported by NIDCD.]
Remote ultrasonic classification of fluids in cylindrical containers by analyzing the response of circumferential guided waves
Authors: Kaduchak Gregory , Sinha Dipen N.
Published: July 2002

A novel technique for classifying fluids in sealed, metal containers at large stand-off distances has been developed. It utilizes a recently constructed air-coupled acoustic array made from inexpensive, commercial-off-the-shelf components to excite the resonance vibrations of fluid-filled vessels. The sound field from the array is constructed by transmitting a high-frequency modulated carrier wave which utilizes the nonlinearity in the air medium to demodulate the carrier frequency along its propagation path in air. The array has a narrow beamwidth and an operating bandwidth of greater than 25 kHz. The vibrations are detected using a laser vibrometer in a monostatic configuration with the acoustic source. It is shown that the propagation characteristics of the ao Lamb wave are highly affected by different interior loading conditions on the interior wall of a cylindrical container. Classification of the interior fluid is obtained by analyzing the change of this response as a function of frequency. Experiments demonstrate that classification of the fluid-filler inside closed, steel vessels is possible with incident sound pressure levels of the demodulated wave as low as 80 dB at the container location. Preliminary experiments demonstrate that stand-off distances greater than 3 m are achievable for classification purposes.
Acoustical free oscillation NDT method of cracks for turbomachinery
Authors: Gelman Leonid M. , Bezvesil’na Olena V. , Gorpinich Sergey V. , Strokov Aleksandr P.
Published: July 2002

A new vibroacoustical nondestructive testing and evaluation method is proposed. The method uses phase spectral density harmonics of testing object free oscillations as features. New analytical expressions of phase spectral density of testing object free oscillations are received and considered.
Training Chinese speakers to perceive English /nl/
Authors: Schmidt Anna M , Kaminski Amy , Chung Hyunjoo
Published: July 2002

Native speakers of some southern Chinese dialects have difficulty perceptually differentiating English /n l /. In this study, five native Chinese subjects participated in a training experiment designed to increase perception of the /n/-/l/ contrast using a fading technique [D. Jamieson and D. Morosan, Percept. Psychophys. 40, 205–215 (1986)]. Stimuli consisted of initial /n/ and /l/ words produced by four native English speakers in which the initial consonants were increased by varying amounts. Subjects were first trained on the longest exemplars, and progressed to the natural versions. Both discrimination and identification training sets were used along with immediate feedback. Pre- and post-training perception generalization and production data were obtained. Results and implications will be discussed.
A computational analysis of uniqueness points for Japanese auditory word recognition
Authors: Yoneyama Kiyoko , Johnson Keith
Published: July 2002

This paper discusses uniqueness points for all words in a 65000-word computerized lexicon in Japanese. The uniqueness point is the point in a left-to-right scan where the word is distinguished from all other words in the lexicon. This is an important concept in the Cohort Theory of auditory word recognition. Four different analyses were conducted based on two variables: the processing unit (segment or mora) and the phonetically transcribed representation (with or without pitch information). The probability of the uniqueness point being prior to the end of the word was highest when pitch information was included and/or when words were represented in segments rather than in moras. Still, in the best combination of variables (segments with pitch information) only 48% of the words reached a uniqueness point before the end of the word. This study predicts that if Japanese listeners use small processing units and attend to pitch, recognition performance will be maximized, but for most words this optimal processing strategy will still result in a Cohort size greater than one at word’s end.
Evidence for the independence of speech categories in perception and production
Authors: Hemphill Rachel
Published: July 2002

Models of speech processing, which attempt to account for speech input and output in phonological or categorical terms, generally rely on one single underlying representation for both perception and production. Previous research by Hemphill [J. Acoust. Soc. Am. 104, 1757–1758 (1998)] has suggested that two separate representations are necessary to account for asymmetries in acquisition data. Sixteen native speakers of English were trained to categorically perceive a three way voicing contrast in Thai bilabial stop consonants. The results of perception and production tests following training indicate that subjects were unable to accurately produce the contrasts that they had learned from perceptual training, despite the fact that they could identify the perceptual stimuli correctly. Additional perception testing after a two-month interval found that subjects were still able to label the training stimuli accurately, but could not identify their own productions with greater accuracy than they identified the training stimuli or the productions of unfamiliar talkers. These results are explained in terms of separate perception and production representations in the mind and an hypothesis about the reorganization of perceptual categories is explored.
Branching and phrasing in Seoul Korean
Authors: Lee Minkyung
Published: July 2002

This paper examines the relationship between the structural composition, the phrasing and duration and pitch range in Korean utterances. Previous linguistic models (Selkirk, 1986) predict that the syntactically left branching (LB) and right branching (RB) structures should correspond to different phrasings, which according to previous phonological models (Jun, 1993, 1995) should be indicated by the presence of rises in fundamental frequency. Speakers were instructed to produce syntactically ambiguous phrases in a frame which highlighted the ambiguity. The experiment indicates that LB and RB cases were collapsed together resulting in the same phrasing. Even though LB and RB structures usually exhibited the same phrasing, speakers did show differences in pitch range and duration which distinguished left from right branching structures. Initial words in RB cases were longer and had a relatively larger pitch range than RB cases. Such effects have also been found as a correlate of focus. Thus speakers tend to express structural properties of utterances by means of phonetic differences in relative peak F0 height and duration, apart from differences in phrasing.
Overlap at the interface: High vowel devoicing in Japanese
Authors: Varden J. Kevin
Published: July 2002

High vowel devoicing (HVD) in Japanese has been characterized as both phonological [J. D. McCawley, The Phonological Component of a Grammar of Japanese (1968)], phonetic due to gestural overlap [S.-A. Jun and M. E. Beckman, LSA Paper (1993)], and as a result of overall vowel reduction [M. Kondo, Ph.D. thesis, University of Edinburgh (1997)]. Electromyographical and laryngeal spread data from one speaker [A. Tsuchida, Ph.D. dissertation, Cornell University (1997)] supports the existence of both phonological and phonetic devoicing in complementary environments, while data from ten speakers [J. K. Varden, Ph.D. dissertation, University of Washington (1998)] indicates the presence of both types of devoicing in overlapping environments. Results of Varden (1998) also indicate high-speaker variability in rate of devoicing, duration of voicing for voiced vowels, and context-dependency. A synthesis of these studies supports a characterization of HVD as the result of varying processes, each having the same acoustic end: the devoicing and overall reduction of high vowels in devoicing environments. The data in Varden (1998) also indicate a high incidence of devoicing of /u/ in the mora [tsu] before /n/ for some speakers. This indicates relaxation of the requirement of a following underlyingly voiceless segment.
Adapting time-frequency responses to speech and acoustic classification tasks
Authors: Atlas Les E.
Published: July 2002

Much past effort, including our own, has gone into the design of high-resolution time-frequency representations. However, as found in most data-trained automatic classification applications, high resolution can significantly degrade performance. This behavior can be understood from the standpoint of complexity: The higher the resolution and complexity of the time-frequency representation, the larger the size of the training data needed for an accurate classifier. For most applications, where many regions in time and frequency are not salient to the classification task at hand, lowering resolution in these regions should actually improve classifier performance and generality. A new time-frequency approach, called ‘‘class-dependent kernels,’’ which selectively smoothes in time and frequency, has been developed. This approach can be summarized by considering the points of a discrete auto-ambiguity function, which is the two-dimensional Fourier transform of a time-frequency representation, as a set of features, which can be ranked in terms of saliency to the particular classification task. Keeping and classifying based on only a small number of these ambiguity plane points corresponds to a flexible and data-adaptive smoothing of the corresponding time-frequency plane. This approach will be shown to be useful for a wide range of acoustic and vibration problems including monitoring acoustic emissions in titanium removal and as an adjunct to cepstra in speaker-independent phoneme recognition.