bluuebunny/crossref_metadata_2025 huggingface dataset:
Rays, modes, and spectra: Footprints in phase space
Authors: Felsen Leopold B.
Published: October 2005

Ray methods have been used extensively to describe mid- and high-frequency, as well as pulsed, phenomena associated with acoustic propagation in the presence of submerged solid or layered elastic structures. The relevant wavefields include externally reflected and diffracted, as well as externally–internally coupled, progressing constituents, repetitive multiples of which combine into oscillatory (modal) forms. Full exploitation of ray methods for radiation and scattering scenarios, either forward (for classification) or inverse (for identification), is aided by systematic footprinting of the (space-time)–(wave number-frequency) characteristics of the various wave objects in a (configuration)–(spectrum) phase space catalog. ‘‘Clean’’ footprints obtained from forward asymptotics for certain test problems are shown to be diffused (a) by windowed processings that are applied to extract these footprints from data (imaging), and (b) by space-time limits imposed on the data set. Examples include submerged elastic cylindrical, and finite flat plate, geometries. Also included are simple models of truncated strict or perturbed periodicity, with illustration of superresolution and backpropagation [L. Carin etal., J. Acoust. Soc. Am. (submitted)]. [Work supported by ONR and AFOSR.]
Postmodern quantum mechanics: Chaos and the Schrödinger wave equation
Authors: Tomsovic Steven
Published: October 2005

Recent theoretical and experimental developments are driving a growing interest in the asymptotic wave behavior of quantum mechanics. The underlying ray theory is based on the trajectories found in the corresponding classical mechanical system. Many systems exhibit some chaotic motion and present a number of challenges for the theory. Recent advances will be illustrated with the stadium billiard which has become one of the premiere paradigms of highly chaotic dynamics [E. J. Heller and S. Tomsovic, Phys. Today 46(7), 38 (1993)]. Both the time-dependent and stationary solutions will be discussed. [Work supported by NSF Grant No. PHY-9305582.]
Bioeffects of positive and negative pressure pulses in vivo
Authors: Bailey Michael R. , Blackstock David T. , Dalecki Diane , Raeman Carol H. , Child Sally Z. , Carstensen Edwin L.
Published: October 2005

Murine lung and Drosophila larvae were used to compare effects of isolated positive and negative pulses on tissue containing gas bodies. The basic pulse, produced by an underwater spark, was positive. It could be isolated by floating absorptive, nonreflecting rubber on the water surface to prevent reflection. When an isolated negative pulse was desired, the rubber was removed and the direct, positive pulse was blocked by inserting a jagged-edge barrier between the spark and the exposure area. The jagged edge rendered the diffracted wave (from the barrier edge) incoherent and therefore negligible in the exposure area. Exposure levels were varied by altering the proximity of the exposure area to the source. For each level, lung damage and larva mortality due to 20-pulse exposures were measured. Positive pulses were found to be at least as damaging, to both tissues, as negative pulses having the same amplitude. If the damage was due to cavitation, this result is contrary to conventional wisdom, which holds negative pressure largely responsible for the violence of inertial cavitation. It is speculated that the expansion and ensuing catastrophic collapse of a bubble are hindered in the presence of tissue. [Work supported by ONR, NIH, and ARL: UT IR&D program.]
Sound transmission to the human fetus
Authors: Morfey Christopher L. , Pinnington Roger J.
Published: October 2005

A common noninvasive test for fetal well-being involves transmitting an audio-frequency acoustic signal into the amniotic fluid by means of a mechanical vibrator, which is applied to the mother’s abdomen close to the fetal head. This test has been simulated in the laboratory, using a silicone rubber model uterus of spherical shape filled with water. The outside of the model was excited by an impedance head and a load-distributing contact disk. Mechanical impedance measurements were compared with similar measurements on volunteer subjects at about 30 weeks’ pregnancy, and showed similar trends as a function of frequency. The model was then used to establish a transfer function between the exciting force and the acoustic pressure in the water-filled cavity. A simple theoretical model is presented which accounts for the main features observed experimentally. Results indicate that commercial fetal stimulators can produce intrauterine sound pressures as high as 30 Pa rms (180 Pa peak pressure) close to the point of excitation. The actual level depends on the thickness of the subcutaneous fat layer which couples the vibrator to the uterus.
Propagation of elastic waves inside concretions to simulate dynamic failure of kidney stones and gallstones during lithotripsy
Authors: Dahake Girish , Gracewski S. M.
Published: October 2005

Reflection and superposition of stress waves is analyzed using finite difference techniques to better understand the effect of stone parameters and geometry on the distribution of strains within kidney stones and gallstones during lithotripsy. Concretions of irregular geometries are subjected to ultrasonic wave sources that simulate lithotripter pulses. The time evolution of strain is calculated inside cylinders of rectangular and circular cross sections, due to an incident radially diverging source in the liquid surrounding the solid. Two schemes are considered to explicitly account for the liquid–solid interface conditions. Both schemes account for varying grid sizes and give identical results for straight interfaces, but the second scheme also handles irregular interfaces. The time sequence obtained numerically for strain at the center of a rectangular cylinder also matches well with the experimental results [S. M. Gracewski etal., J. Acoust. Soc. Am. 94, 652–661 (1993)]. In addition, strain contours are plotted for the propagation of P (longitudinal) and SV (shear vertical) waves inside a circular cylinder. It is shown that the reflection from the concave back surface of the circular cylinder has a focusing effect with the subsequent formation of focal zones (caustics).
The propagation of ultrasonic waves through a bubbly liquid into tissue: A linear analysis
Authors: Qi Quan , Harris John G. , O’Brien William D.
Published: October 2005

The steady-state response induced by an ultrasonic wave in a structure comprised of two layers, a bubbly liquid, and a viscoelastic solid with a rigid boundary, is studied in the linear approximation. This structure models a steadily cavitating liquid in contact with tissue. The upper surface of the liquid is driven harmonically and models the source. The lower surface of the solid is rigid and models bone. Though the cavitation processes are nonlinear, the propagation is approximated as linear. The model of the bubbly liquid is a simple continuum one, supplemented by allowing for a distribution of different bubble radii and for damping of the oscillations of each bubble. The model contains three functions, the probability distribution describing the distribution of bubble radii, and two functions modeling the mechanical response of, respectively, the individual bubble and the tissue. Numerical examples are worked out by adapting data taken from various published sources to deduce the parameters of these functions. These examples permit an assessment of the overall attenuation of the structure, and of the magnitude of the pressure and particle velocity in the bubbly liquid, and of the traction and the particle displacement in the tissue. [Partial support from Arjo, Inc., Morton Grove, IL.]
Cavitation from short pulses high-frequency ultrasound: A study of cavitation production rates and their dependence on acoustical parameters
Authors: Calabrese Adam , Roy Ronald A.
Published: October 2005

Previously, cavitation due to pulsed megahertz-frequency ultrasound was detected using a technique that only looked for the onset of detectable cavitation [Calabrese etal., AdvancesinNonlinearAcoustics, edited by H. Hobæk, pp. 394–399 (1993)]. This method provides little information about cavitation production rates, which may be better correlated to a mechanical bioeffect than the threshold alone. A modified approach using a passive cavitation detector [Roy etal., J. Acoust. Soc. Am. 87, 2451–2458 (1990)] is used to determine the rate of cavitation as a function of acoustic pressure amplitude. Measurements are repeated for a variety of pulse lengths (from 3 to 100 μs) and duty cycles (from 0.1% to 20%) and at frequencies of 1, 2.25, and 5 MHz. Initial results suggest that the threshold pressure for cavitation is weakly dependent on pulse length and decreases with increasing duty cycle. [Work supported by NIH through Grant No. RO1 CA39374.]
Focused acoustic pulses of finite amplitude and their influence on cavitation bubble dynamics
Authors: Averkiou M. A. , Crum L. A. , Hamilton M. F.
Published: October 2005

A computer code that solves the KZK equation in the time domain [Lee and Hamilton, UltrasonicsIntl. 91 ConferenceProceedings (Butterworth-Heinemann, Oxford, 1991), pp. 177–180] is modified to include the effects of focusing on pulsed sound beams of finite amplitude. Single cycle pulses, similar to those used in lithotripsy and high intensity focused ultrasound (HIFU) surgery, are considered. The numerical results demonstrate the combined effects of nonlinearity, absorption, diffraction, and focusing on the waveform distortion and shock formation in short acoustic pulses. Self-defocusing associated with shock formation is also taken into account. Propagation curves are shown for the positive peak pressure amplitude (P+) and the negative peak pressure amplitude (P−) along the axis of the source. The calculated pressure waveforms are used as input to computer codes that model bubble dynamics. Predicted radius-time curves are presented for the response of a bubble due to a focused acoustic pulse of finite amplitude. Gas diffusion from the liquid into the vapor bubble, and the roles of P+ and P− in the diffusion process, are also considered. [Work supported by the National Institute of Health.]
The biological relevance of transient cavitation measurements performed in water: The effect of shear viscosity
Authors: Allen John , Roy Ronald A.
Published: October 2005

Recent years have seen a host of direct experimental evidence of transient microcavitation in water produced by short pulses of megahertz-frequency ultrasound [Roy etal., J. Acoust. Soc. Am. 87, 2451–2458 (1990); and others]. However, to our knowledge there have been no published accounts of direct observations of such microcavitation activity in biological media. It is useful to relate the results of the aqueous experiments to the likelihood of producing cavitation in tissue. To do this, one must assess the relevant differences between the two media. As a first step in this process, a numerical implementation of the Gilmore equation for adiabatic bubble pulsations is employed [Church, J. Acoust. Soc. Am. 83, 2210–2217 (1988)] and compare predicted thresholds in water and in biological media modeled as a viscous fluid. Comparisons are made with the analytical theory of Holland and Apfel [IEEE UFFC 36, 204–208 (1989)]. The requirement that, at the threshold pressure, the bubble collapse temperature exceed 5000 K provides the rigorous comparison criterion. Results are viewed in light of recent experimental results obtained in water [Calabrese etal., J. Acoust. Soc. Am. 95, 2856 (1994)] and in tissue-mimicking phantom materials [Zheng etal., J. Acoust. Soc. Am. 95, 2855 (1994)]. [Work supported by NIH through Grant No. RO1 CA39374.]
Development of 1–3 and 2–2 piezocomposite transducers
Authors: Bowen Leslie , Gentilman Richard , Pham Hong , Serwatka William , Fiore Daniel
Published: October 2005

1–3 and 2–2 piezoelectric ceramic/polymer composites offer design versatility and performance advantages over monolithic piezoelectric ceramic and monolithic piezoelectric polymer devices in both resonant and nonresonant transducer applications. Recently, a new process, viz., ceramic injection molding, has been applied to solve the difficulties of cost-effectively manufacturing the arrays of fine PZT ceramic elements required for composite transducer assembly. As a result, these materials are now available in commercial quantities for the first time. In this paper, Materials Systems, Inc. briefly introduces its PZT ceramic injection molding transducer manufacturing process, and then reviews the performance of various 1–3 composite transducer designs as a function of composite layout, materials, and transducer performance enhancement features, such as stiff cover plates and Poisson’s ratio decoupling. The performance of several transducer designs in both nonresonant sensing and actuating undersea applications, and in high-frequency resonant applications, e.g., acoustic imaging, is discussed. [Work supported by ONR.]
Surface-mounted sensors on a large-area 1–3 composite actuator
Authors: Corsaro Robert D. , Houston Brian
Published: October 2005

Surface-mounted sensors can be used to monitor the performance of an underwater acoustic projector, or to control its impedance in a complex dynamic environment. However, there are few examples in the literature of studies of the issues involved in marrying sensors and actuators. These issues include spatial sampling, near field sensing, internal resonances, and both direct and extraneous coupling mechanisms, all of which can contribute to complicate the system transfer functions and limit the applicability of this approach. The work presented here includes measurements made on a 1–3 composite actuator with integrated pressure and velocity sensor layers. Both free-field sensitivities and actuator–sensor coupling transfer functions are evaluated in the NRL Large Pool Facility. These are compared with predictions from simple acoustic models. Implications for local control of the actuator’s surface are also discussed.
A dynamic model for piezoelectric composite transducers and coupling coefficient k
t
Authors: Shui Yongan , Xue Qiang
Published: October 2005

Piezoelectric composite materials are increasingly used in medical and other ultrasonic transducers. In order to design composite transducers with desirable performance, especially in high-frequency range where polymer and ceramic structures are not much smaller than wavelength, a good understanding of dynamic behavior of the material is necessary. This work developed a dynamic model to investigate wave propagation along thickness direction and resonant behavior of the transducer. Relationships of thickness resonant frequencies as well as lateral periodic resonant frequencies with composite configuration and material (polymer and ceramic) properties were emphasized. Discussions on coupling coefficient kt of transducers as a function of volume fraction and aspect ratio of composite are presented. A series of composite transducers with varied parameters were fabricated and measured. Experimental results of kt and resonant frequencies are compared with the theory.
Influence of dynamic absorbers on a three-dimensional truss
Authors: Branthonne Denis , Dyer Ira
Published: October 2005

The objective of this research is to explore experimentally the effects of adding dynamic absorbers to a three-dimensional truss and to design analytical models which predict the phenomena of attenuation. The truss is built with cells made of aluminum rods and connected in series. 110 dynamic absorbers are mounted on the rods in the center cell to achieve a local mass ratio of 3. The truss is excited at one end with white noise to measure the spatial attenuation averaged on octave bands as a function of axial distance. The data are compared to the spatial attenuation for the undamped structure. The differences determine the effect of the dynamic absorbers. The overall shape of the differential curves of attenuation versus axial distance is a step function, with the step located in the dynamic absorbers attachment area. Assuming the equipartition of energy between the different wave types and using the classical theory of attenuation of waves propagating on a semi-infinite rod loaded with a continuous layer or dynamic absorbers, one predicts stronger attenuation than experimental data at low frequencies. The assumption of equipartition of energy proves to be incorrect and the applicability of the semi-infinite model is questioned. Subsequently, a new theory is derived and validated by experiment to describe the attenuation of waves on finite rods loaded with a layer of dynamic absorbers. At low frequencies, this model achieves a better estimation of the axial attenuation along the truss. [Work supported by ONR.]
The effect of surface characterization and laser beams polarization on laser Doppler vibrometry
Authors: Yang Ming , Jarzynski Jacek , Berthelot Yves H.
Published: October 2005

In a laser Doppler vibrometry, the characterization of the measured surface plays an important role in both in-plane and out-of-plane surface motion measurements. Experimental data is presented for the in-plane optical probe configuration, where the vibrating surface is illuminated symmetrically by two laser beams. However, some of the conclusions of the present study apply also to out-of-plane vibration measurements. It is found that certain surfaces perform better than others. How the surface character affects the in-plane surface motion measurement (in particular, the signal-to-noise ratio and the probe alignment) is studied. The surfaces studied are lathe-finished, polished aluminum and steel surfaces and two types of retroreflecting tapes from 3M company. Also, the profiles of the metallic surfaces are obtained with a profilometer. A simple model is used to relate the surface characteristics to the performance of in-plane motion measurement. The effect of polarization of the two laser beams is also studied, including the depolarization of the light by the surface. [Work supported by ONR.]
Dispersion of longitudinal waves in periodic septate liquid–elastic waveguides
Authors: Sheiba L.
Published: October 2005

The propagation of longitudinal waves in a composite liquid–elastic waveguide is analyzed. The waveguide is a periodic structure consisting of alternating liquid–elastic cylinders joined by rigid septa. The elastic material (Lamé constants: μ≪λ, Poisson relation σimplies0.5) and the liquid material (μ=0, σ=0.5) are assumed to have low compressibility, and the septa are rigid and weightless. Consequently, the boundary between the cylinder and the septum’s radial displacement is absent, and the axial displacements are planar. The admittance matrix Y of the unit cylinder is initially constructed within a framework of the hypothesis of plane cross sections, neglecting strains induced by hydrostatic stress. Hydrostatic stress waves are approximately included by adding to the unit cylinder admittance matrix correction ΔY associated with the strains of hydrostatic stress in the cylinder. Transfer matrix of the liquid–elastic waveguide and its elements, expressed through the waveguide sections elastic parameters, have been obtained. It has been shown that damping in a waveguide with a periodic structure is much greater in comparison with a regular waveguide, even when the latter is made with a high-loss material.
A new method for damage detection in structures using transient bending wave propagation
Authors: Ting K.-L. , Li Zongabo
Published: October 2005

With the increasing demand for safety and reliability on structures and mechanical systems, damage detection by nondestructive evaluation (NDE) methods has attracted considerable attention from many researchers. This paper presents a new method for damage detection based on time-frequency analysis of transient bending wave propagation. The wavelet transform and short-time Fourier transform are applied to the analysis of impulse-induced bending wave propagation in a cracked finite beam. The time-frequency representation resulting from the transformation of measured acceleration response is utilized to identify the reflection part of the transient bending wave by a crack and to determine its reflection coefficient and the arrival time (from the location of the crack to the transducer position) for different frequency components contained in the transient bending wave. The quantity of the crack is evaluated from the reflection coefficient, and its location is estimated from the arrival time. To demonstrate the effectiveness of the presented method in quantifying and locating cracks, a cantilever beam and a free–free beam with the same crack are investigated.
Recognition of speech separated from acoustic mixtures
Authors: Cooke Martin , Green Phil
Published: October 2005

A perceptually plausible solution to the problem of automatic recognition of speech in arbitrary noise backgrounds involves computational auditory scene analysis (ASA) followed by recognition of the separated patterns. However, it is not generally possible to recover a complete representation of individual acoustic sources, so a new approach is required to recognize partial descriptions. Suitable modifications to the powerful stochastic framework of hidden Markov models (HMM) have recently been described [M. P. Cooke, P. D. Green, and M. D. Crawford, Proc. Int. Conf. Spoken Language Processing (1994)]. The studies reported here demonstrate HMM-based digit recognition in noise. An auditory-nerve firing rate representation undergoes auditory scene analysis, producing a mask of time-frequency locations where the speech is dominant. Each mask frame defines a marginal distribution for the HMM probability calculation. Results show robust performance even when the mask has most of its elements removed. Further, these studies suggest a solution to the problem of sensitivity to F0 in matching auditory representations of speech in which F1 is represented by a set of resolved harmonics. The new approach ensures that the matching process operates on a partial description consisting largely of harmonic peaks.
Processing of continuous speech by a hierarchical neural network
Authors: Brandt Wolf Dieter , Behme Holger
Published: October 2005

A multilevel neural network has been developed for the tasks of psychoacoustic preprocessing of speech, segmentation, segment classification, and recognition. Various neurophysiological and psychoacoustical results have been taken into account. The network relies heavily on unsupervised learning. On increasing and nonlinear time scales, each level of the network extracts segments from the stream of input data and classifies them using topology-conserving vector quantizers (self-organizing feature maps SOFM, ‘‘neural gas’’ algorithm (NGA) and passes the results to the next level. Modified learning algorithms for feature maps have been developed to achieve better representation of low-energetic consonants and transient parts in the first level. On higher levels variants of the NGA are used. The segmentation algorithm uses, depending on the level, the topological relationships within the SOFM or statistical information extracted from the training data. Within each segment, dynamic time normalization is achieved by appropriate temporal integration. The output of the topmost level is passed to a recognition network containing a linguistic model to perform continuous speech recognition. Results using this purely neural and in many parts self-organizing method will be presented and compared to classical methods. [Work supported by BMFT.]
Calculation of a source spectrum using matched-field tracking
Authors: Bucker Homer
Published: October 2005

An underwater acoustic source can be detected by finding the best match between a measured set of covariance matrix elements and those calculated for possible tracks [H. Bucker, ‘‘Matched-field tracking in shallow water,’’ J. Acoust. Soc. Am. (to be published)]. Let (glft) be the measured elements and (ĝlft) be the elements calculated for the best track of a unit source. Here, index l refers to a pair of sensors, f to a frequency bin, and t is for different times. Then a plot of S(f,t)=∑lglft/∑lĝlft is a Lofargram in which the effects of the multipath propagation have, at least in part, been removed. Of course, the success of the deconvolution depends upon the accuracy of the propagation model and contamination of other sound sources. Several examples will be presented to illustrate the method.
Acoustic array navigation in shallow water
Authors: Gingras D. F. , Troiano L. , Williams R. B.
Published: October 2005

The inversion of acoustic field data for estimation of unknown environmental or geometric parameters is receiving considerable attention. The environmental parameters usually consist of bathymetry, sound speed in the water, and bottom properties such as sound speed, attenuation, and density. The geometric parameters consist of source and array sensor positions. In many situations it is assumed that the array sensor positions are known and in these cases it is important to the inversion process that the array sensor positions are known precisely. In this paper an acoustic navigation method for precisely determining sensor position is presented. Acoustic travel time measurements were used to navigate the sensors of a 94-m vertical array in shallow water (130 m). Array navigation performance was evaluated during a vertical array deployment in the Mediterranean from the R/V Alliance. A network of four bottom-moored acoustic transponders were interrogated from the Alliance and their replies were received by the vertical array sensors and telemetered to the Alliance and their replies were received by the vertical array sensors and telemetered to the Alliance for navigation processing. In October, over a 2-day period, current versus depth and array shape was monitored. During this period the local currents were small; the array shape was estimated to be almost straight and nearly vertical.
Effects of aircraft noise on wildlife: Techniques used in Air Force research
Authors: Kull Robert C.
Published: October 2005

Many researchers have set out to study the effects of noise on animals, especially aircraft noise, for the past 20 years yet have failed in properly describing the noise their subject animals were exposed to. In 1989 the Air Force began a series of wildlife studies to determine the effects of aircraft noise. Research included effects on Desert Bighorn Sheep, caribou, kit fox, domestic turkeys, dairy cows, horses, and raptors. One major objective in these studies was to accurately determine the noise exposure levels from aircraft. Conventional methods were used for research on domestic animals, but studies on wild animals posed special problems. Various techniques and procedures of how noise exposures were determined will be described.
Physiological monitoring of noise effects in wildlife
Authors: DeYoung D. W. , Kull R. C.
Published: October 2005

Noise as a stress to animals will be discussed with respect to the physiological parameters that characterize it. Known currently available radiotelemetry systems that can monitor some of these parameters will be presented. Data that can be reliably derived from parameters obtained by available radiotelemetry systems will be presented. Possible pathology due to long-term stress as well as information for animal studies, telemetry implant surgery and anesthesia, and the potential complications of implant surgery will be discussed. Finally, recommendations for future study of noise as a stressor to animals will be made. [Work supported by USAF.]
Passive acoustic localization of calling animals in 3-D space
Authors: Spiesberger John L.
Published: October 2005

Fluctuations and uncertainties in winds (currents) and sound speed place lower limits on the accuracy with which calling animals can be passively localized from their calls in terrestrial and marine environments. The most accurate acoustic passive localizations of animals require simultaneous mapping of these environmental fluctuations using tomographic techniques [J. Spiesberger and K. Fristrup, Am. Nat. 135, 107–153 (1990)]. One localization experiment conducted in a wood found tomographic localization of a cap gun possible but tomographic localization of birds difficult because of echoes. Marine environments may be conducive to tomographic localizations because of a paucity of reflecting surfaces at low frequencies. A new oceanographic instrument called a surface suspended acoustic receiver (SSAR) has the potential for passively localizing and censusing calling animals throughout the world’s oceans in real time. [Work partially supported by Advanced Research Projects Agency.]
Hot topics in acoustical oceanography
Authors: Crum Lawrence A. , Buckingham Michael J.
Published: October 2005

Since acoustical oceanography was given full Technical Committee status within the ASA in November 1991, there has been a rapid development of novel techniques for interrogating the ocean using sound. For example, the total global precipitation amount is poorly known; however, by examining the underwater noise produced by rainfall, it may be possible to use underwater acoustic monitoring devices to obtain an estimate of this precipitation and from that better estimates of the global heat flux. Recently, it has been demonstrated that the sound pulses can be propagated over extremely large distances in the ocean; consequently, a precise timing of the arrival of these sound pulses over extended periods would enable changes in the average ocean temperature to be monitored, and thus provide information on global warming. Similarly, ambient noise provides the basis of a new acoustic imaging technique, designated acoustic daylight, that is analogous to conventional photography but based on sound rather than light. These and a variety of other topics will be presented.
Event-related vertex potentials preceding vowel onset
Authors: Holland Nancy , Yonovitz A.
Published: October 2005

Neural events prior to speech were determined by averaging vertex-recorded potentials 512 ms before vocalization. In a manner analogous to auditory-evoked potentials, it would seem plausible to identify specific sites along motor pathways that yield cortically recordable electrical potentials that are precursory to vocalization. In this study, subjects repeatedly phonated a schwa 500 times. The repetition rate was approximately 8/min with the subject initiating each trial. The onset of vocalization was detected by a throat microphone that provided the trigger. The sample rate (25 000 samples/s) was sufficient to observe brief time periods (10 ms) along the averaged prespeech time epoch. The results indicated that repeatable, biphasic potentials were obtained during the time period between 45 and 250 ms before the onset of the vowel trigger. Interwave latencies between wavelets were highly related within and between subjects. The technique of event-related potentials may be a useful procedure for studying the electrophysiology of speech production in normal and disordered speakers.
Acoustic phase stability in a shallow-water environment
Authors: Mire Christine T. , Stanic Stephen
Published: October 2005

The formation of a synthetic aperture is dependent on the phase stability of the medium. Temporal and spatial phase stability of the medium were estimated from measurements taken during a high-frequency experiment conducted in August 1993 in the shallow-water coastal environment off Panama City, Florida. Phase stability was estimated from sequences of 150 0.5-ms and 1.0-ms pulses separated by 1-s intervals at experimental frequencies of 20, 40, 60, and 90 kHz. Phase fluctuations were found to contain both deterministic and random components which changed with time, indicating a changing propagation environment. Phase fluctuations were spatially correlated between both vertical and horizontal components of the receiving array. The relationship between acoustic phase stability and environmental factors is examined. Results of this analysis are compared with previous phase stability measurements [J. T. Christoff, C. D. Loggins, and E. L. Pipkin, J. Acoust. Soc. Am. 71, 1606–1607 (1982); P. T. Gough and M. P. Hayes, ibid. 86, 837–839 (1989)]. [Work sponsored by ONR.]
Acoustic pulse to pulse variability due to seawater temporal temperature fluctuations
Authors: Zhang Li , Goodman Ralph , Stanic Steve
Published: October 2005

Mire and Stanic (preceding abstract) have observed significant pulse to pulse fluctuations in high-frequency seafloor backscattering measurements in which the sound sources and receivers were mounted on a tower that stood on the seafloor in a shallow-water environment (about 30 m). This paper presents the hypothesis that temperature fluctuations that are associated with turbulence can account for the acoustic variability. The model is based on a random distribution of fixed discrete scatters on the surface of the seafloor. Computations that sum the arrivals of scattered CW pulses for a range of changes in travel times that are due to varieties in the average temperature along the paths reveal fluctuations similar to Mire and Stanic’s observations for a range of tens of meters, temperatures changes as small as a tenth of a degree Celsius, and frequencies of about 40 kHz and higher. Comparisons between computations and measurement are presented in this paper. [Work supported by NRL/Stennis.]
Laboratory measurements of variability in high-frequency bottom backscatter due to thermal fluctuations
Authors: White P. Jason , Gilbert Kenneth E. , Goodman Ralph R.
Published: October 2005

From the World War II era to the present, researchers in ocean acoustics have observed fluctuations (scintillation) in high-frequency backscatter from the seafloor. In general, the fluctuations have been regarded as a nuisance to be gotten rid of if possible. Here the possibility that the fluctuations may actually provide a means to learn more about the scattering process than would be possible with an unchanging signal is considered. Laboratory experiments are described in which known targets are insonified in the presence of artificially induced thermal fluctuations. The resulting backscattered signals are discussed and analyzed within the framework of a weak scatter theory. Possible applications to ocean data are pointed out. [Work supported by ONR and NRL.]
Acoustic backscatter analysis from a smooth sand surface
Authors: Laughlin Julia , Chotiros Nicholas P.
Published: October 2005

A multiscattering theory to describe backscatter behavior in water-filled sands has been developed for smooth sand surfaces. The theory is based on a two-dimensional solution of the diffusion equation and a Biot propagation theory for porous materials. Experiments were conducted at high frequencies (80–120 kHz) to measure backscatter at shallow grazing angles from smooth sand surfaces at varied sand depths. In addition, reflection measurements were made at normal incidence to verify the smoothness of the sand surface. Comparisons of theoretical model backscatter results to experimental measurements were then made. [Work supported by ONR, Ocean Acoustics Program, Code 11250A.]
The effect of gradients on high-frequency bottom scattering
Authors: Moe John E. , Jackson Darrell R.
Published: October 2005

The first-order perturbation expression for the bistatic scattering cross section of a rough surface [Moe and Jackson, J. Acoust. Soc. Am. (to be published)] is used to study the effect of gradients on high-frequency bistatic bottom scattering. Strong gradients on scales of several centimeters are often observed in shallow-water environments. It is shown that upward refraction or reflection by strong gradients can lead to significant enhancement of high-frequency scattering. This enhancement occurs over a wide range of bistatic angles, but is strongest when the incident and scattered grazing angles are equal. These effects can be explained in terms of the reflection coefficient of the corresponding mean (flat) surface. [Work supported by ONR.]
Temporal coherence and stability of bottom interacting sound pulses
Authors: Tang Xin , Tappert Fred D.
Published: October 2005

Sound propagation at moderate frequencies (depth to wavelength ratio between 20 and 100) in shallow-water environments is extremely complicated, variable, and poorly understood due to multiple processes that cover a wide range of temporal and spatial scales. Broadband full-wave numerical simulations are performed with the UMPE model at a large number of geophysical times to display the temporal variability, stability, and coherence of acoustic pulse arrivals in a multipath environment that includes multiple rough bottom forward scattering and multiple forward volume scattering by internal waves that are described by either a Garrett–Munk type of spectral model or a soliton type of model. It is found that the effects of rough bottom scattering change the phase structure while the effects of internal waves account for the observed temporal fluctuations, leading to coherence times of minutes for individual multipaths at 20-km ranges, and a stable envelope having a coherence time of hours. [Work supported by ONR.]
Shallow-water backscatter reduction through selective mode excitation
Authors: Gingras D. F.
Published: October 2005

In shallow-water areas the utilization of active sonar is complicated by the fact that in these environments the performance of active sonar systems is degraded by backscatter generated by source signal interaction with channel boundaries. In this paper knowledge about the shallow-water acoustic channel, namely the normal-mode structure, is used to design vertical source arrays which minimize source signal boundary interaction. The boundary signal interaction is minimized for many environments by exciting only the first mode. Mode one excitation is accomplished by weighting the array sources by the amplitude and polarity of the mode one eigenfunction. Simulations across the frequency range from 200 to 700 Hz using a two-way PE backscatter model were conducted. It was shown that a vertical array of sources, containing only 15 elements, can reduce bottom generated backscatter by as much as 15–20 dB.
Formant movement and duration cues in the identification of vowels
Authors: Neel Amy T. , Kewley-Port Diane
Published: October 2005

Traditionally, target values of F1 and F2 are viewed as primary determinants of vowel identity. Several recent studies, however, have demonstrated the importance of dynamic formant information to vowel identification. The present study examines the contribution of both dynamic and durational information to vowel identification using sine-wave vowel analogs. Sine-wave stimuli consisting of two tones representing F1 and F2 were constructed using careful LPC measurements of ten vowels produced in /dVd/ context by male and female speakers. Four types of stimuli were constructed by varying two factors: (1) appropriate versus fixed vowel duration and (2) variation in tones representing formant movement throughout the token versus static target formant values. Listeners identified the sine-wave vowel analogs using a key-word response form. Results demonstrated that stimuli with appropriate vowel duration were identified with significantly greater accuracy than those with fixed length. For appropriate duration stimuli, there was no significant difference for dynamic versus static tokens. However, for fixed length stimuli listeners identified dynamic tokens with significantly greater accuracy than static stimuli. This suggests that intrinsic vowel duration, as expected, is an important cue to vowel identity and that dynamic formant information is used more by listeners when duration cues are unavailable.
A linear model of boundary shifts in /v–i/ and /open oh–eh/ continua
Authors: Nabelek Anna K. , Ovchinnikov Alexandra
Published: October 2005

Boundary locations were tested for /v–i/ and /open oh–eh/ continua with steady-state or linearly changing formants in which F2 was varied. F1 and F2 trajectories had upward and downward directions. Boundary shifts were calculated for changing formant stimuli relative to the boundary for steady-state stimuli. The directions of boundary shifts indicated perceptual emphasis of the final segments of F2 trajectory which might be a consequence of low-frequency spread of masking from F1 to F2. A linear model was developed in which boundary shifts were related to spectral distance between F1 and F2 trajectories. Parameters were initial and final frequencies of F1 and boundary F2 established for each continuum with steady-state stimuli. When the distance was constant in time shifts depended on directions of F1 and F2 trajectories, described by two model terms containing differences of initial and final frequencies of F1 and F2. When the distance was changing in time additional shift was toward the greater spectral distance, described by two model terms containing ratios of initial and final frequencies. [Work supported by NIH.]
The spectral center of gravity effect and auditory filter bandwidth
Authors: Fagelson Marc , Thibodeau Linda M.
Published: October 2005

The spectral center of gravity refers to a listener’s averaging of frequency and intensity components when formant peaks in a speechlike signal are separated by 3.5 Bark units or less. In this paper a total of 18 synthetic vowels whose spectra approximated /ae/ or /inverted vee/ were generated digitally; each stimulus contained the first 40 harmonics of a 100-Hz fundamental. Nine spectra contained three formants, while the balance contained only two. Subjects with normal hearing and mild high-frequency hearing loss above 3000 Hz were instructed to identify synthetic vowels as either /ae/ or /inverted vee/ as F2 frequency was varied between nine different values in 100-Hz steps for both the two-formant and three-formant stimuli. Probit analysis indicated that the normal-hearing subjects identified stimuli more consistently than the mildly hearing-impaired listeners across F2 frequencies for three-formant than for two-formant spectra. The F2 frequency corresponding to the perceived increase in vowel frontness occurred at a lower frequency for normal-hearing listeners. Auditory filter bandwidth was negatively correlated with the F3−F2 Bark difference. Results suggest that spectral averaging may help listeners disambiguate confusing speech signals.
The effects of duration changes on the perception of vowel sequences
Authors: Chalikia Magdalene H. , Dresser Tammy
Published: October 2005

Previous studies have shown that listeners exposed to a repeated sequence of steady-state vowels (of same duration and pitch) experience phonemic transformations, and report hearing words and phrases absent in the original stimulus. A previous study [M. H. Chalikia, R. Meyer, and R. Lindemann, 34th Psychon. Society Meet. (1993)] investigated the possible effects of variations in vowel duration. Duration variations ranged from 30 to 120 ms per vowel. Listeners successfully matched these stimuli to the verbal forms heard with vowels of equal duration and pitch, confirming the robust, stable nature of the verbal organizations. It was suggested that these organizations are based upon objective acoustic characteristics, and the stimulus manipulations were probably perceived as prosodic variations. In this study a broader variation in duration was employed (10–300 ms), in an attempt to examine listeners’ limitations in performing the matching task. Six base-line sequences of six 80-ms vowels (at 100 Hz), followed by a 300-ms silent gap, were used. Four variations of these were created by randomly changing the duration of individual vowels within a sequence. Most listeners were not able to perform the task. Implications concerning the perceptual organization of speech will be discussed.
Target response measurement system for the NUWC Lake Seneca Test Facility
Authors: Deveau David M. , Carlton Lynn F. , Stein Peter J.
Published: October 2005

Here is presented an overview of the target response measurement system (TRMS) deployed at the NUWC Seneca Lake test facility. This system is capable of measuring the target strength of objects at ranges from 10 to 300 m. The frequency range for monostatic measurements is from 300 Hz to 400 kHz. The current bistatic capability is measurements every 5° over a 90° window from 2 to 15 kHz. A multichannel PC-based digital data-acquisition system has been developed which includes high-speed A/D boards, baseband translation, and real-time monitoring of TS as a function of target aspect angle. Target aspect angle and acoustic source signatures are measured at the target and telemetered to the acquisition for digital storage along with the acoustic data. Accuracies of 1 dB in TS and 1° resolution in target aspect angle are possible. Measurements are generally clutter limited to a target strength less than −30 dB re: 1 m. Clutter of the target harness is usually a major issue and is discussed. The target strength of various targets and support structures is presented.
Wideband reverberation reduction in long-time acoustic signals produced by transducers in small test chambers
Authors: Winsor Niels K. , Hess Gary R. , White Forest E. , Young Chris M. , Roberts Russ
Published: October 2005

For times long compared to the acoustic wave transit time in a test tank, the signal from point acoustic sources may be dominated by internal reflections and the modal response of the experimental tank in which experiments are performed. If the free-field source behavior of the acoustic source is desired, it can be extracted by taking advantage of special properties of the source/tank system. The transducer can be operated in a manner which permits characterization of the tank response; then the processed results can be used to reduce the effects of the tank response in the signals of interest. Spectral methods for this signal processing will be described and illustrated. The result is that signal characteristics in spectral regions of interest can be more clearly resolved and enhanced. [Work sponsored by U.S. Navy.]
Determination of effective piston area by three methods
Authors: Garrett S. L. , Gaitan D. F.
Published: October 2005

The volumetric velocity of an acoustic source is sufficient to characterize its source strength if the acoustic impedance of the load presented to the source is known. Although a calibrated accelerometer can accurately determine the velocity of a piston, the volumetric velocity requires a determination of the effective area of the ‘‘piston.’’ For a thermoacoustic refrigerator operating at resonance, this load is purely resistive. Three methods for determining the effective area of an electrodynamic thermoacoustic driver will be presented. For insitu measurements, good agreement (±2%–4%) was obtained between direct measurement of the force, using the known Bl product and the resonant reciprocity method using the transfer impedance calculated by Rudnick [G. W. Swift, A. Migliori, S. L. Garrett, and J. C. Wheatley, Rev. Sci. Instrum. 53, 1906–1910 (1982)]. The result for effective area obtained by measurement of pressure under the reactive load presented by a small coupler [T. Hofler, J. Acoust. Soc. Am. 83, 777–786 (1988)] was smaller and more pressure dependent. A possible explanation for this discrepancy, based on bellows deformation under different loading, will be presented. [Work supported by ONR, the Naval Postgraduate School Direct Funded Research Program, and the Navy Science Assistance Program.]