bluuebunny/crossref_metadata_2025 huggingface dataset:
Pulsed signal propagation on a one-dimensional random waveguide—A numerical simulation
Authors: McCoy John J. , Tanzosh John
Published: October 2005

A numerical simulation of the following experimental scenario is accomplished. A pulse, narrow in space/time, is incident upon a spatially irregular, piecewise-homogeneous transition interval of finite length in an otherwise homogeneous waveguide of unbounded length. The characterization narrow implies an extent that is small when compared to the lengths/transit times for the homogeneous segments. One, of several, result of interest is a demonstration that an ensemble averaged, or mean, field description of this experiment should accommodate two pulsed coherent signals to exit the transition layer. The first signal ‘‘propagates’’ with a velocity that can be identified with an averaged wave speed. This signal decays rapidly with increasing length of the transition interval as a result of scattering, and spreads, in general, due to variation in propagation speed across an ensemble of transition intervals. The genesis of this first pulse is the ‘‘primitive’’ pulse that transmits every interface in the transition interval. The second mean-field pulse propagates with an ‘‘effective,’’ or composite material, wave speed. The genesis of this second pulse are a large number of primitive pulses, all of which have suffered a large number of reflections at the internal interfaces of the transition interval.
Helium effects on the click frequency spectrum of the Harbor porpoise, P
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Authors: Amundin Mats
Published: October 2005

In order to determine in which medium, air or tissue, harbor porpoise (Phocoena phocoena) sounds are produced, the air in the nasal cavities was substituted with heliox (80% helium and 20% oxygen), and the effect on click frequency spectrum was studied. The sound speed is 1.86 times higher in heliox than in air and the resonance frequency of a fixed cavity filled with heliox is increased by this factor as compared to that of the same cavity filled with air. The harbor porpoise emits click sounds restricted in the frequency domain to two relatively narrow bands, one around 2 kHz and one in the 120- to 140-kHz range. The results show that the stronger high-frequency component was not at all affected by the heliox, suggesting that it was produced and shaped in some tissue structure(s), and not in gas. The low-frequency component obviously was affected by the heliox, although the frequency rise did not match the expected theoretical factor. This was probably due to simultaneous, uncontrolled changes in cavity volume, interfering with the heliox effect. It is concluded, however, that the low-frequency component was a gas bound phenomenon, taking place in the nasal pathways. The results also show that the stronger high-frequency component always occurred together with and in the beginning of the low-frequency component, indicating that both were the result of the same production event. These results are in line with previous observations of air bound click sounds being heard when porpoises phonated with open blowhole, and of simultaneous vibrations occurring in the upper nasal passways, in the tissues containing the right dorsal bursae.
Noise exposure from leisure activities: A review
Authors: Clark William W.
Published: October 2005

Over the past two decades there has been increasing concern about the role of nonoccupational, or leisure noise on hearing. This paper reviews published studies that detail the noise levels and potential effects of some noisy leisure activities. Considered are the most common sources of leisure noise: exposure to live or amplified rock, classical, or jazz music; exposures from personal listening devices (‘‘walkman’’ type); noise around the home, and hunting and target shooting. Although all activities listed above have the potential for dangerous levels of noise exposure, the most serious threat to hearing comes from recreational hunting or target shooting.
The scanning acoustic microprobe: I. Analysis and synthesis of a spherically symmetric point spread function
Authors: Barber Frank E.
Published: October 2005

The scanning acoustic microprobe is a novel system which probes and characterizes, from a limited acoustic window, the fine-scale structural features of an object, point-by-point, using a multiplicity of acoustic pulses all aimed and focused at that point. Spherically symmetric, three-dimensional Gaussian pulses are synthesized to measure the backscatter diffraction pattern of the least-resolvable volume of scatterers centered at the point in question. The size and distribution of the scattering volume is forced to be constant, independent of frequency and angle. This method is analytically simple, compared with other pulse-echo techniques, and is applicable to scatterers ranging continuously in size from Rayleigh scatterers to specular reflectors. This is the first of a number of papers describing the development and application of systems based on these concepts. The analytical principles will be described herein for examination of one point at a time. In a companion paper appearing in this issue [F. E. Barber, J. Acoust. Soc. Am. ▪▪, ▪▪▪–▪▪▪ (1991)], application to measurement and characterization of a discrete, flat, circular ‘‘piston’’ will be presented. Application to human tissue imaging and tissue characterization will be described in a subsequent third paper. The primary features detected experimentally are the strength of nondirective patterns, and the strength, orientation, and directivity of angle-dependent echo functions associated with planar or layered structures. Fine-scale structural features of a scattering center are obtained either by pattern recognition in k(data) space or inverse Fourier transformation. It is shown that when the bandwidth criteria are met to produce a spherically symmetric point spread function, scattering phenomena are completely described by only two parameters, namely the center frequency of the pulse-echo system and the characteristic diameter of the Gaussian point spread function.
The effect of pure-tone forward masking on overshoot
Authors: Hicks Michelle L. , Bacon Sid P.
Published: October 2005

The overshoot effect can be reduced by temporary hearing loss induced by aspirin or exposure to intense sound. The present study simulated a hearing loss at 4.0 kHz via pure-tone forward masking and examined the effect of the simulation on threshold for a 10-ms, 4.0-kHz signal presented 1 ms after the onset of a 400-ms, broadband noise masker whose spectrum level was 20 dB SPL. Masker frequency was 3.6, 4.0, or 4.2 kHz, and masker level was 80 dB SPL. Subject-dependent delays were determined such that 10 or 20 dB of masking at 4.0 kHz was produced. In general, the pure-tone forward masker did not reduce the simultaneous-masked threshold, suggesting that elevating threshold with a pure-tone forward masker does not sufficiently simulate the effect of a temporary hearing loss on overshoot.
Phenomenological characterization of eardrum transduction
Authors: Shera Christopher A. , Zweig George
Published: October 2005

A phenomenological description of the transduction effected by the eardrum is presented. That description is provided by a transfer matrix, whose elements define those measurements sufficient to characterize eardrum transduction. Causality provides constraints on the matrix elements. In addition, measurements of the matrix elements can determine whether they satisfy constraints imposed by minimum-phase behavior and the principle of reciprocity. Those constraints may be used either to reduce the number of measurements necessary to characterize the eardrum or to check the consistency of measurements that overdetermine the system. Within its region of validity, the transfer matrix of the eardrum provides a common ground for the comparison between theory and experiment. As an example, a simple model for the transduction characteristics of the eardrum, defined completely in terms of measurable quantities, is presented.
Designing quantitative echo sounders
Authors: Furusawa Masahiko
Published: October 2005

A procedure for designing quantitative echo sounders, whose main purpose is fisheries resource surveys, is described. The quantitative echo sounder must be designed under the specific criteria, such as minimum error, taking into account the purpose, external conditions, and several acoustic characteristics. The acoustic characteristics needed in the design procedure, for example, the scattering properties of fish, are reviewed briefly. In the main part, the method to determine the pulse width, bandwidth, operating frequency, transducer diameter, and gain allocation for each stage of the receiver is described. A convenient ‘‘universal diagram’’ is introduced for determining the basic parameters. The diagram serves also for users of sounders. Application of the method to two kinds of sounders is demonstrated. The optimum frequency for quantitative echo sounders is discussed and the frequency of 38 kHz, being used worldwide, is shown to be a reasonable frequency.
Factors that influence rate-versus-intensity relations in single cochlear nerve fibers of the gerbil
Authors: Ohlemiller Kevin K. , Echteler Stephen M. , Siegel Jonathan H.
Published: October 2005

The relationship between characteristic frequency (CF) and rate-intensity curve shape was examined in 144 cochlear nerve fibers obtained from 39 Mongolian gerbils. Quasi-steady-state firing rates were measured in response to tone bursts at the CF. From each intensity curve, estimates of slope, firing rate at saturation, and dynamic range were derived using nonlinear curve fitting. Saturation firing rate was depressed for stimuli with a high duty cycle, especially for units with low rates of spontaneous discharge. The distributions of slope and saturation firing rate differed for fibers with CFs above and below 3 to 4 kHz. The interrelation of slope, dynamic range, maximum driven rate, and spontaneous firing rate was also different for fibers with CFs above and below this band. This mid-CF transition is discussed in terms of possible longitudinal changes in the function of the gerbil cochlea.
Use of large bandwidth-duration binary phase shift keying signals in target delay Doppler measurements
Authors: Jourdain G. , Henrioux J. P.
Published: October 2005

Some classes of signals exhibiting a good delay-Doppler power resolution (ambiguity function) in active radar/sonar cases, and particularly in the case of true Doppler effect (compression ambiguity function), are discussed. Large WT BPSK signals are presented, which are the most performant in this sense, and are compared with more classical signals. A further improvement is given by amplitude modulation. Some examples are given of target parameters measurements achieved by using these signals, and especially by using the differential range and Doppler measurements. Some simulations are presented, and also some real underwater acoustic target measurements.
Assimilation and contrast in the phonetic perception of vowels
Authors: Shigeno Sumi
Published: October 2005

The perceptual mechanisms of assimilation and contrast in the phonetic perception of vowels were investigated. In experiment 1, 14 stimulus continua were generated using an /i/–/e/–/a/ vowel continuum. They ranged from a continuum with both ends belonging to the same phonemic category in Japanese, to a continuum with both ends belonging to different phonemic categories. The AXB method was employed and the temporal position of X was changed under three conditions. In each condition ten subjects were required to judge whether X was similar to A or to B. The results demonstrated that assimilation to the temporally closer sound occurs if the phonemic categories of A and B are the same and that contrast to the temporally closer sound occurs if A and B belong to different phonemic categories. It was observed that the transition from assimilation to contrast is continuous except in the /i′/–X–/e/ condition. In experiment 2, the total duration of t1 (between A and X) and t2 (between X and B) was changed under five conditions. One stimulus continuum consisted of the same phonemic category in Japanese and the other consisted of different phonemic categories. Six subjects were required to make similarity judgements of X. The results demonstrated that the occurrence of assimilation and contrast to the temporally closer sound seemed to be constant under each of the five conditions. The present findings suggest that assimilation and contrast are determined by three factors: the temporal position of the three stimuli, the acoustic distance between the three stimuli on the stimulus continuum, and the phonemic categories of the three stimuli.
Anticipatory velar lowering: A coproduction account
Authors: Bell-Berti Fredericka , Krakow Rena Arens
Published: October 2005

Feature spreading and coproduction models make fundamentally different assumptions about the nature and organization of speech motor control, and yet each model is supported by some, but not all, of the existing empirical data. This has led some researchers to conclude that speakers probably use alternative strategies at different times. This study suggests that the identification of coarticulatory influences requires the concurrent identification of intrinsic articulatory characteristics of the segment. Moreover, the evidence for feature spreading or variable coarticulation strategies derives from the misidentification of such intrinsic characteristics as context effects. This velar coarticulation study used a controlled comparison between CVnN and CVnC minimal pairs, where C is an oral consonant, Vn is any number of vowels, and N is a nasal consonant. Vocalic string duration was manipulated by varying the number of segments and speech rate, allowing us to alter the time between the onsets of vocalic and subsequent consonantal gestures. Velar lowering occurred in CVn sequences, whether or not a nasal consonant followed, and similar vocalic gestures were observed across minimally contrastive environments with and without the nasal consonant. Moreover, velar lowering for the nasal consonant began in close temporal proximity to the nasal murmur. These results strongly support the coproduction model and provide insight into previously conflicting reports.
The scanning acoustic microprobe: II. Application to the measurement and characterization of a piston reflector
Authors: Barber Frank E.
Published: October 2005

In a pulsed ultrasound beam, echoes detected from a flat, circular piston of arbitrary size depend on the time-space characteristics of the entire pulse-echo measurement system, being a function of as many parameters as it takes to accurately define the system. In the limiting case of a target that is small relative to the spatial extent of an interrogating plane wave, an echo pattern is known to be a relatively simple function of the dimensionless product k0b, where k0 is the wave number and b is the radius of the target. In a companion paper preceding this one [F. E. Barber, J. Acoust. Soc. Am. 90, 8–17 (1991)], the author has described the scanning acoustic microprobe, a pulse-echo system in which the time-space properties of the interrogating waves are specified completely by k0 and a single additional parameter s0, which is the characteristic radius of a spherically symmetric, Gaussian-distributed scattering volume. In this system, the reflection pattern of a flat, circular piston of any arbitrary size is thus a function of two dimensionless parameters, namely k0b and b/s0. In this paper, this functional relationship is derived, a physical system is described, and analytical and experimental results are reported. It is shown that the diameter, orientation, and impedance mismatch properties of this simple target can be measured unambiguously over a range of target sizes from about a wavelength (2π/k0) to a beam diameter (about 3s0 ). For a typical ultrasound system, this is about a 5–1 range; i.e., a range extending to target sizes about five times smaller than can be detected in a simple B-mode imaging system. Theoretical and experimental results are described and discussed in detail. The implications of such a system for quantitative analysis of more complex target structures and constituents are explored. The methods lead naturally to a new technique for imaging that will display fine-scale features not seen by any other method.
The effects of external- and middle-ear filtering on auditory threshold and noise-induced hearing loss
Authors: Rosowski John J.
Published: October 2005

A model of external- and middle-ear function is described that uses existing data to quantify the flow of sound power from the environment to the cochlea of humans, cats, and chinchillas. This model estimates the sound power produced at the entrance of the cochlea by an environmental sound stimulus, and can be used to predict the shape of the auditory threshold function and the relative potency of various traumatic acoustic stimuli. The shapes of the predicted and measured threshold functions in the three species are similar in best frequency, bandwidth, and low-frequency slope, and the model accurately predicts the hypersensitivity of the middle-frequency regions of the cochlea to acoustic trauma. The model assumes that the mechanics of the middle-ear system are linear even at high stimulus levels and does not include the effects of either middle-ear or cochlear efferent loops. The effects of these simplifications on the model are discussed as are the implications of the model results for hearing protection and damage risk criteria.
Analysis of the scattering of a plane acoustic wave by a doubly periodic structure using the finite element method: Application to Alberich anechoic coatings
Authors: Hladky-Hennion Anne-Christine , Decarpigny Jean-Noël
Published: October 2005

The finite element approach has been previously used, with the help of the ATILA code, to model the scattering of acoustic waves by single periodic structures, such as compliant tube gratings [A. C. Hennion et al., J. Acoust. Soc. Am. 87, 1861–1870 (1990)]. In this paper, the same approach is extended to doubly periodic structures, such as Alberich anechoic coatings. To do this, only the unit cell of the periodic structure, including a small part of the surrounding fluid domain, has to be meshed, due to the use of classical Bloch type relations. Then, the effects of the remaining fluid domain are accounted for by matching the pressure field in the finite element mesh with simple plane-wave expansions of the ingoing and outgoing waves. After an outline of the method, the paper describes the results obtained for the scattering of a plane wave by different periodic structures. Internal losses are taken into account and the incident plane wave impinges at normal or oblique incidence. Numerical results obtained for Alberich anechoic coatings are first analyzed to check the convergence and then compared to previous numerical results or to experimental results, demonstrating that the finite element approach is accurate and well suited to predict the behavior of these gratings. Moreover, careful attention is devoted to the analysis of the inclusion vibrations, to identify the origin of the resonance mechanisms.
Active suppression of acoustic radiation from impulsively excited structures
Authors: Baumann William T. , Saunders William R. , Robertshaw Harry H.
Published: October 2005

The objective is to use active control to suppress the acoustic energy that is radiated to the far field from a structure that has been excited by a short-duration pulse. The problem is constrained by the assumption that the far-field pressure cannot be directly measured. Therefore, a method is developed for estimating the total radiated energy from measurements on the structure. Using this estimate as a cost function, a feedback controller is designed using linear quadratic regulator theory to minimize the cost. Computer simulations of a clamped–clamped beam show that there is appreciable difference in the total radiated energy between a system with a controller designed to suppress vibrations of the structure and a system with a controller that takes into account the coupling of these vibrations to the surrounding fluid. The results of this work provide a framework for a general, model-based method for actively suppressing transient structural acoustic radiation that can also be applied to steady, narrow, or broadband disturbances.
General formulation of thermoacoustics for stacks having arbitrarily shaped pore cross sections
Authors: Arnott W. Pat , Bass Henry E. , Raspet Richard
Published: October 2005

Theoretical treatments of thermoacoustics have been reported for stacks with circular pore and parallel plate geometries. A general linear formulation is developed for gas-filled thermoacoustic elements such as heat exchangers, stacks, and tubes having pores of arbitrary cross-sectional geometry. For compactness in the following, F represents the functional form of the transverse variation of the longitudinal particle velocity. Generally, F is a function of frequency, pore geometry, the response functions and transport coefficients of the gas used, and the ambient value of the gas density. Expressions are developed for the acoustic temperature, density, particle velocity, pressure, heat flow, and work flow from knowledge of F. Heat and work flows are compared in the short stack approximation for stacks consisting of parallel plates, circular, square, and equilateral triangular pores. In this approximation, heat and work flows are found to be greatest for the parallel plate stack geometry. Pressure and specific acoustic impedance translation theorems are derived to simplify computation of the acoustical field quantities at all points within a thermoacoustic engine. Relations with capillary-pore-based porous media models are developed.
Mechanical characterization of a unidirectional composite by ultrasonic methods
Authors: Wooh Shi-Chang , Daniel Issac M.
Published: October 2005

The anisotropy of fibrous composite materials makes it difficult to determine their elastic constants nondestructively. Quantitative ultrasonic methods were studied to determine elastic constants of a transversely isotropic laminate. Comprehensive relationships of the measured ultrasonic data and material properties were developed. The mode conversion phenomenon at the specimen–liquid interface with oblique incidence ultrasonic immersion testing provided all the necessary information. Determination of elastic constants was possible by measuring wave speeds and critical angles. Phase velocities were determined by the multiple reflection technique utilizing ultrasonic spectroscopy. A special scanning technique was developed to determine the phase velocities and wave propagation angles in the anisotropic plane from the measured group velocities. The method developed was applied to the characterization of a unidirectional graphite/epoxy composite.
Portable device for real-time administration of a branching questionnaire.
Authors: Fidell Sanford , Brockett Douglas , McCraw Michael
Published: October 2005

Conventional methods for assessing community response to aircraft noise, such as social surveys, are optimized for recording delayed self-reports of long-term opinions about cumulative exposure. Although prompt reactions to individual aircraft noise intrusions may also be of concern in some settings, lack of cost-effective apparatus has limited the ability to collect such information. One obstacle has been the lack of a convenient means for administering a branching questionnaire in real time to people in field settings. An ongoing independent research and development project has developed a prototype version of a digital device suitable for inclusion in a ‘‘Talking Hat’’ that can ask questions and recognize ‘‘yes’’ and ‘‘no’’ answers to them.
Absolute calibration of hydrophones.
Authors: Bacon David R.
Published: October 2005

Ultrasonic fields in the megahertz frequency range are normally characterized using hydrophones, since they are readily available and can measure the spatial and temporal distribution of acoustic pressure. To give absolute results, however, the hydrophone’s response needs to be measured as a function of frequency. Ideally, the amplitude and phase response should be known in the frequency range 0.3–100 MHz. At the National Physical Laboratory (NPL), four methods have been used for calibration−planar scanning, two-transducer reciprocity, laser interferometry, and the so-called magnomic method. Planar scanning and reciprocity agree with the results of other techniques in the range 0.5–15 MHz, but they are increasingly difficult to apply at frequencies above 10 MHz. Laser interferometry is the primary method used at NPL and gives overall uncertainties at the 95% confidence level of between 2.5% and 5% over the frequency range 0.3–20 MHz. The magnomic method has recently been used to measure the amplitude and phase response from 5 to 100 MHz. The results are in agreement with the interferometric method at low frequencies and with predictions of the frequency response of the hydrophone at higher frequencies. NPL has recently been the pilot laboratory for a European intercomparison of calibrations (funded by the Community Bureau of Reference) in which four other laboratories participated. The results of this comparison will be described briefly.
Optical fiber sensors for absolute calibration of ultrasound.
Authors: Jarzynski J. , Bucaro J. A. , Lagakos N. , DePaula R. P.
Published: October 2005

Detection of ultrasound with an optical fiber sensor was first studied by DePaula etal. [IEEE J. Quantum Electron. QE-18, 680 (1982)]. A single-mode fiber was used to detect ultrasound, and a theoretical model was developed for the fiber-optic ultrasonic sensor. The incident ultrasound changes both the phase and the polarization of the light in the fiber, and either of these effects can be used to sense the ultrasound. The advantages of fiber sensors for calibration of ultrasound are as follows: (1) excellent reproducibility, linearity, and absence of aging effects; (2) the physical dimensions of the fiber are small and it does not disturb the ultrasonic field; and (3) the fiber sensor is broadband (0.1 MHz to above 50 MHz), and has a large dynamic range. More recently Chiang etal. [J. Lightwave Technol. 8, 1221 (1990)] have studied detection of ultrasound with polarization maintaining fibers. These fibers are less sensitive to environmental noise, and require a simpler detection circuit when configured as sensors. This paper reviews fiber-optic ultrasonic sensors. The topics include estimates of the sensitivity and dynamic range of the sensors, and discussion of the various available detection schemes. Also presented will be the results of recent work on development of a theoretical model for the interaction of ultrasound with light in polarization-maintaining fibers.
Absolute calibration of ultrasonic fields using a submersible electrostatic acoustic transducer.
Authors: Yost William T. , Cantrell John H.
Published: October 2005

The development of a liquid-immersible, megahertz-range, electrostatic acoustic transducer (ESAT) was previously reported [Cantrell etal., Rev. Sci. Instrum. 50, 31–33 (1979)]. The transducer basically consists of a thin conductive membrane stretched over an electrically isolated cylindrical electrode recessed approximately 10 μm from the membrane inner surface. A model recently developed to explain the frequency roll-off characteristics of the ESAT resulting from liquid-membrane coupling [J. H. Cantrell and W. T. Yost, Rev. Sci. Instrum. 60, 487–488 (1989)] together with a Thevenin equivalent substitutional circuit scheme permits absolute measurement of ultrasonic displacement amplitudes in the submicron range to be made with the ESAT. The geometry of the system allows straightforward correction for diffraction effects. ESAT calibration of ultrasonic tone bursts generated by broadband piezoelectric transducers immersed in water is reported. A fast Fourier transform-based technique using short unipolar voltage excitation for piezoelectric transducer calibration is discussed. [Work supported by NASA Office of Technology Utilization.]
Measurement of the angular spectrum of ultrasonic transducers using an optical probe.
Authors: Hays-Stang Kathy J. , Johansen Michael , Cook Bill D.
Published: October 2005

In the Raman–Nath region of ultrasonic light diffraction (i.e., at frequencies near 1 MHz and narrow sound beam width), a laser light beam can be configured to be a line receiver of the ultrasound. With care, both the phase and magnitude of the integral of the pressure along the line can be extracted as an electric signal from a fast-responding photodetector. By means of an optical lens, the photodetector can be effectively placed near or inside the sound field. At this close proximity, the measurement system is linear. Making measurements where the laser beam is placed at positions along a line from above to below the sound beam yields information that constitutes a ‘‘projection’’ of the soundfield. Taking the spatial Fourier transform then yields a slice of the angular spectrum. The experimental system is described and examples of the measured angular spectrum are shown.
Using an optical probe to investigate pulsed ultrasonic fields.
Authors: Johansen Michael , Hays-Stang Kathy J. , Cook Bill D.
Published: October 2005

For continuous waves, a laser-beam probe can be configured with a photodetector to be a line detector of pressure in an ultrasonic field. It is important that this detector behaves in a linear manner. For this linearity, the experimental configuration includes filtering the electrical signal from the photodiode. This filtering eliminates the second and higher harmonics caused primarily by the optics and secondarily by the harmonics in the sound field. This convenience is not available for pulsed ultrasonic waves where the spectrum is wide. Such a filter would remove the part of the pulse. Moreover, the size of the fast-responding photodetector becomes important at the higher frequencies cutting off where the wavelength of the sound and the size of the photodetector are comparable. These and other limitations of the laser optical probe define a limited range where such a laser-beam probe can be used.
Spectral interference in a binaural detection task: Effects of temporal fringe and masking bandwidth.
Authors: Bernstein Leslie R. , Trahiotis Constantine
Published: October 2005

Recently, it was reported that the detection of a 100-ms, 800-Hz tone (the target), in the NoSπ configuration was degraded by about 4–7 dB when a 400-Hz tone (the interferer) was gated simultaneously with the target against a background of continuous, broadband noise. [L. R. Bernstein, J. Acoust. Soc. Am. 89, 1306–1313 (1991)]. This ‘‘interference’’ was reduced substantially by presenting the interferer continuously. In the present study, the amount of interference was measured when (1) the interferer was gated prior to the target and (2) when the target was surrounded by a 100-Hz-wide band of noise, thus allowing for a larger masking-level difference. Although important individual differences were observed, the data suggest that the 400-Hz interferer must precede the target by 160 to 320 ms in order for the interference observed to be essentially equivalent to that obtained with a continuous interferer. Surrounding the 800-Hz target by narrow-band rather than broadband noise yielded only slight increases in the amount of interference. [Work supported by AFOSR and NIH.]
Sensitivity to level differences as a function of duration.
Authors: Florentine Mary , Buus So/ren
Published: October 2005

The purpose of this study was to determine how the sensitivity, d’, for level discrimination (also known as intensity discrimination) grows with increasing stimulus duration. The method of constant stimuli was used to measure performance in a 2I,2AFC task with feedback. Stimuli were tones ranging from 0.25 to 14 kHz and broadband noise. Levels ranged from 30 to 90 dB SPL. For each stimulus, the level difference, ΔL {=20 log[(p+Δp)/p], where p is pressure}, and stimulus power were kept constant while duration varied from 2 to 2000 ms. Results from three normal ears showed that d’ increases as a power function of duration up to some critical duration. The exponents average about 0.25 for stimuli with excitation patterns less than 7 Barks wide and about 0.35 for stimuli with excitation patterns wider than 7 Barks. These exponents are in good agreement with our earlier results for difference limens [M. Florentine, J. Acoust. Soc. Am. 79, 792–798 (1986)] and indicate that d’ grows more slowly than the square root of duration. A possible explanation for this finding is that adaptation in the auditory nerve reduces the information for level discrimination over time. Accordingly, ‘‘looks’’ late in a long-duration stimulus contribute less to performance than looks early in the stimulus. [Work supported by NIDCD.]
Classification of heterogeneous seafloor topography through surface slope distributions.
Authors: Shaw Peter R. , Smith Deborah K.
Published: October 2005

Seafloor topography is neither spatially homogeneous, nor does it obey Gaussian statistics; deviations from both of these assumptions are important from a geological and acoustic point of view. It has been found that the distribution of topographic slopes can be used as a primary tool for understanding the sources and extent of spatial heterogeneities and patterns on the seafloor. The covariance function has been widely used to characterize seafloor topography, but requires the assumption of Gaussian joint probability statistics to be valid. For heterogeneous topography characterized by large transient signals such as steep scarps and volcanoes, the covariance becomes dominated by the transients; in contrast the family slope distributions can still be used to derive stable descriptors for regions with large transient signals, as well as regions containing asymmetric features, and regions with only limited sampling. Knowledge of slopes is useful because a direct relation exists between the covariance and the slope distributions at different spatial scales. Studies of the slope distribution provide a means of identifying the presence of the non-Gaussian elements in the topography, and flagging their spatial locations. The methods used here are demonstrated by applying them to three small patches of topography located within 20 km of each other in the Eastern Pacific. It is found that dominant azimuthal directions and dip angles differ widely between the patches. In addition, asymmetries in the cross-sectional shapes of faulted abyssal hills are documented. [Work supported by ONR.]
A review of low-frequency seafloor reverberation measurements.
Authors: Goodman Ralph R. , Zhang Li
Published: October 2005

Measurements of reverberation from the seafloor are of use in both theoretical models of scattering as well as for developing an empirical basis for systems development and operation. It is useful to review, therefore, the experimental results that are used for these purposes. The experiments that are most often cited span about the past 30 years. The most common techniques utilize omnidirectional sources and receivers near the sea surface or near the seafloor. Recently, results have been reported that utilize directional arrays. Both broadband and narrow-band sources have been used. The results of several experiments are examined and compared. The backscattering strengths as a function of grazing angle are compared, based on frequency and geological similarity (wherever possible). The search for the elusive ‘‘Lamberts law’’ will be discussed. Frequencies up to about 3 kHz are considered.
Effect of waveheight spectrum on 2-D Rayleigh–Rice perturbation theory.
Authors: Pourkaviani M. , DeFerrari H. A. , Willemsen J. F.
Published: October 2005

Time-dependent and static Rayleigh–Rice perturbation theory is examined for a two-dimensional sea surface using waveheight spectrum proportional to K–γ for large values of K. The range of values for γ considered here is between 2.5 and 5.0, and the only constraint imposed on waveheight spectra is that all different values of γ should yield the same rms height for a given wind velocity. Numerical results for a range of frequencies, wind velocities, and grazing angles are presented for backscattering, and in the static case comparisons are made with Chapman and Harris results. [Work supported partly by the Office of Naval Research, Code 1125OA.]
Spatially explicit models of fish production: The integration of acoustics and bioenergetics.
Authors: Brandt Stephen B.
Published: October 2005

Acoustic sensors provide detailed information on biological structure in the sea at relatively fine spatial and temporal scales of resolution. Using a newly developed acoustic visualization and information retrieval (AVAIR) system, this acoustical information is more fully exploited by coupling acoustic data on prey sizes and density and measures of the physical habitat with species-specific bioenergetic models of fish growth rate. The result is a two-dimensional spatial model of fish growth rate potential and system production that has statistical properties and dynamics that differ from those of the underlying physical and biological structure of the system. Given the nonlinearity of most biological processes (growth, production, foraging, behavior), it is argued that such spatially (and temporally) explicit modeling is necessary to link biological processes to physical and biological structure and to predict how changes in patterning and scaling of the environment might affect such higher-order features of the environment.
Subjective response of primary school teachers to noise.
Authors: García A. , Romero J. , García A. M. , Faus L. J.
Published: October 2005

During recent decades some effort has been devoted to determining the effects of environmental noise on schools. Most of these investigations are based on the subjective responses given by teachers to a specific questionnaire. Teaching implies relying on speech communication, which is strongly affected by noise even at relatively low sound levels: In a background noise of 45 dBA and above, teachers increase their vocal effort at a much higher rate than other people do in face-to-face conversation. The study of the effects of interfering noise on educational activities and their relationship to classroom acoustical conditions should provide valuable information for the planning and design of new school buildings and for the improvement of existing ones. As a contribution to this program, this paper reports the first results of a survey carried out in 44 primary schools in Valencia (Spain), covering a wide range of conditions. The attitudes of teachers to noise have been investigated in using the responses to a questionnaire containing 28 different questions. A total of 400 completed forms has been analyzed. The results of the survey show that environmental noise may be a serious problem in many Spanish schools.
Perceptual separation of simultaneous complex tones: The effect of slightly asynchronous onsets.
Authors: Vos Joos
Published: October 2005

Onset asynchrony has been put forward as one of the relevant factors in auditory scene analysis [for references, see A. S. Bregman (MIT, Cambridge, 1990)]. In the present study this issue was investigated further using a new paradigm: Subjects were presented with two successive pairs of simultaneous complex tones and they had to decide whether the pairs contained tones with the same pitch. If this was the case they had to indicate which tones had been equal in pitch [the lower (LL), the higher (HH), the higher in the first pair and the lower in the second pair (HL), or vice versa (LH)]. In experiment 1, the frequency interval between L and H varied between 150 and 750 cents, and in the asynchronous conditions the onset of H was delayed by 20 ms. In experiment 2 various musical intervals were used that were either pure or slightly mistuned, and in the asynchronous conditions the onset of H preceded that of L by 25 ms. The results showed that for the degree of onset asynchrony investigated, no general evidence for a facilitative effect on perceptual separation could be found.
Second language vowel perception.
Authors: Blankenship Barbara
Published: October 2005

This study explored the relation between first language (L1) and second language (L2) vowel perception using synthesized front vowel stimuli that varied in F1 and F2. Bilinguals identified vowel sounds in their L1 (Spanish) and L2 (English) on different days. Individuals’ responses provided English and Spanish F1×F2 maps of the front vowel space that could be compared to each other and to the maps of Spanish monolinguals to determine whether bilinguals have separate perceptual maps for each language, whether age at L2 acquisition or length of L2 use affects the maps, and whether L2 acquisition alters the L1 map. The results indicate that L1 and L2 maps of early L2 learners are more distinct from each other than those of late L2 learners. This finding supports the hypothesis that there is a critical age after which the sounds of a language cannot be learned authentically. No support was found for the notion that L2 acquisition affects L1 perceptual targets. An interesting peripheral finding is that bilinguals can produce vowel distinctions that they cannot perceive in isolated synthesized vowels.
Effects of token variability on resolution for vowel sounds.
Authors: Uchanski R. M. , Millier K. M. , Ronan D. E. , Reed C. M. , Braida L. D.
Published: October 2005

Variability in the production of speech elements complicates the recognition problem for both humans and machines. Paradoxically, variability from token to token of a given speech sound also makes it possible to discriminate between fixed tokens of the sound. Although some components of this variability have no linguistic significance, they may serve as cues when identifying or discriminating specific vowel tokens. The results are reported of identification and discrimination experiments in which the number of tokens used to represent each speech sound was varied. The speech sounds consisted of ten monophthongonal vowels spoken by a single speaker in /h/–V–/d/ context. Generally measures of resolution for vowel contrasts decrease as the number of tokens increases, but the reduction is greater when the number of tokens is increased from one to four than from four to sixteen. The analysis suggests that when one or four tokens of each vowel are used in discrimination tasks, listener judgments are based on perceptual qualities specific to the tokens rather than to general characteristics of the vowels. [Work supported by NIH.]
Acoustic scattering models of zooplankton.
Authors: Stanton Timothy K. , Chu Dezhang , Foote Kenneth G.
Published: October 2005

Quantitative analysis of echoes from marine organisms such as zooplankton can only be possible with the use of accurate acoustic scattering models. In order to describe the scattering of sound by organisms, their size with respect to acoustic wavelength, shape, orientation, and material properties must be taken into account. In this talk, zooplankton backscatter data collected from a variety of investigators in both the laboratory and field are presented. The data are compared with single realizations and averages of the scattering predicted by the deformed cylinder model [T. K. Stanton, J. Acoust. Soc. Am. 86, 691–705 (1989)] and indicate that the animals behave acoustically as weakly scattering fluid elongated objects. The accuracy of current predictions is discussed. [Work supported by ONR.]
Two-frequency plankton biomass estimation.
Authors: Holliday D. V.
Published: October 2005

In a recent meeting of scientists associated with the Global Ocean Ecosystems (GLOBEC) program, a recommendation was made for the development of improved quantitative methods for combining acoustic backscattering information from more than one frequency. An algorithm for combining volume scattering strength data from two frequencies [C. F. Greenlaw, Limnol. Oceanogr. 24, 226–242 (1979)] has been applied to several data sets collected with the Multifrequency Acoustic Profiling System (MAPS) [Pieper etal., J. Plankton Res. 12, 433–441 (1990)]. In MAPS data, the scattering is usually dominated by zooplankton. The result of estimating biovolume versus depth using data from only two of the MAPS frequencies is compared to the estimate obtained by using all 21 frequencies. [Work jointly supported by NSF Biological Oceanography and by ONR Oceanic Biology.]
Impingement tones of axisymmetric choked jets on small plates.
Authors: Henderson Brenda , Powell Alan
Published: October 2005

The impingement of axisymmetric choked jets on normal flat plates produces discrete frequency tones. These tones fall into two classes: tones for small plates and for large plates (A. Powell and B. Henderson, ‘‘On the tones of round choked jets impinging on normal flat plates,’’ AIAA Paper 90-3985). In the case of small plates, the flow is steady when the plate position is such that tones are not produced although the regular shock cell structure is always altered, with the shock wave sometimes being eliminated. The production of small plate tones appears to be associated with large movements of the standoff shock wave in front of the plate, perhaps analogous to the Hartmann oscillator. The dominant upstream propagating waves appear to originate from the flow near the edges of the plate, where periodic(?) disturbances are clearly visible. The downstream propagating waves are more planar and may originate from a different region. The spread angle of the flow downstream of the plate is greatly reduced when small plate tones are produced [Work supported by a NASA fellowship and the Texas Advanced Research Program.]
Fluttering instability in a liquid sheet with acoustic feedback.
Authors: Casperson Lee W.
Published: October 2005

This study focuses on a fluttering instability that can affect a falling liquid sheet. Small displacements of the surface of the liquid may be amplified by the Helmholtz instability mechanism, and naturally occurring acoustic feedback in some configurations can lead to sustained oscillations. The fluttering oscillations have been observed in the free-falling water sheets of several dams and artificial waterfalls, and depending on their scale have been considered to be either attractive or objectionable. The author was recently able to conduct detailed experiments on two large waterfall fountains in Dunedin, New Zealand, and many different oscillation modes were observed. In addition to periodic motions, these interesting dynamical systems can exhibit such effects as mode-hopping, hysteresis, and chaotic behavior. This report includes video pictures of these oscillations and the first model describing the small amplitude dynamics of such a system. Numerical solutions of the differential equations are summarized and compared with experimental behavior. The results should make it possible to design large fountains that are not susceptible to the instability, or alternatively to design small systems that exhibit the instability in its most striking forms.