bluuebunny/crossref_metadata_2025 huggingface dataset:
Diffracting nonlinear Rayleigh wave beams
Authors: Shull D. J. , Kim E. E. , Hamilton M. F. , Zabolotskaya E. A.
Published: October 2005

Nonlinear Rayleigh wave beams in isotropic solids are investigated analytically and numerically. Diffraction effects are taken into account within the parabolic approximation, and nonlinearity is taken into account with a theoretical model used previously to investigate plane and cylindrical Rayleigh waves of finite amplitude [Zabolotskaya, J. Acoust. Soc. Am. 91, 2569–2575 (1992)]. The model equation is expressed in both and time and frequency domains. Quasilinear solutions are presented for second harmonic generation in Gaussian beams, both unfocused and focused. Asymptotic formulas are presented for the second harmonic component in the far field of an arbitrary directive source. Waveform distortion and shock formation are described with numerical solutions for radiation from a source having a uniform amplitude distribution. The numerical results characterize both the near-field and far-field regions of the beam. Numerical results for radiation from uniform sources were presented earlier at 13th ISNA in Bergen, Norway [Shull etal., in AdvancesinNonlinearAcoustics, edited by H. Hobæk (World Scientific, Singapore, 1993), pp. 496–501]. We conclude that the main effects of diffraction can be predicted within the existing theoretical framework for nonlinear sound beams in fluids. [Work supported by the David and Lucile Packard Foundation and by ONR.]
Answer to criticism of my treatment of nonscattering of sound by sound
Authors: Westervelt Peter J.
Published: October 2005

Following a suggestion by Professor M. Korman, the transient solution of an undamped oscillator as a simple analogy to ρs=−Ẇ being the solution of ⧠2(ρs+Ẇ)=0 has been used. Berntson etal. [J. Acoust. Soc. Am. 86, 1968 (1989)] criticized the solution stating that solutions to the homogeneous equation need to be appended in order to satisfy boundary conditions. This is not the case here. Say the forcing function F(t) for the oscillator mẍ+kx=F(t) is derivable from F(t)=mG̈(t)+kG(t) then x(t)=G(t). As an example, if the arbitrary transient starts at t0 and ends T later then G(t)=[U(t−t0)−U(t−t0−T)]H(t) and F(t)= m[δ̈(t−t0)−δ̈(t−t0−T)]H(t)+2m[δ̇(t−t0) −δ̇(t−t0−T)]Ḣ(t)+[U(t−t0)−U(t−t0−T)] [mḦ(t)+kH(t)]. Let us obtain the solution for the case H(t)=b, a constant. In this case F(t)=f1(t)+f2(t), where f1(t)=bk[U(t−t0)−U(t−t0−T)] and f2(t)=bm[δ̈(t−t0) −δ̈(t−t0−T)]. f1(t) is a square wave and the response to it is x1(t)=bU(t−t0)(1−cos ω0t) for t0<t<t0+T and x1(t)= bU(t−t0−T)[cos ω0(t−t0−T)−cos ω0(t−t0)] for t≳t0+T. In f2 the δ̈ generate displacement boundary conditions and x2(t)=bU(t−t0)cos ω0(t−t0) for t0<t<t0+T while x2(t)=−bU(t−t0−T) ×[cos ω0(t−t0−T)] at t≳t0+T.

The complete solution x=x1+x2 is x(t)=0 for t<t0, x(t)=bU(t−t0) for t0<t<t0+T and x(t)=0 for t≳t0+T confirming the fact that x(t)=G(t). This one-dimensional analogy confirms the fact that there is no response outside the interaction region t0<t<t0+T.
Answer to criticism of experiments on the scattering of sound by sound
Authors: Westervelt Peter J.
Published: October 2005

On page 1982 of their article, Berntson etal. [J. Acoust. Soc. Am. 86, 1968 (1989)] criticized virtually all experimental results on the scattering of sound by sound. In addition they gave their necessary conditions for this scattering to be observed. These conditions were fulfilled in a recent experiment [R. Roy and J. Wu, in Proceedingsofthe 13thISNA, edited by H. Hobæk (Elsevier Science, London, 1993)] where no scattered sound was obtained in spite of the fact that the minimum detectable signal level was of the order of 50 dB below Ingard and Pridmore—Brown’s theoretical predictions. The one-dimensional treatment given in the previous abstract to two space-time dimensions will be discussed further.
A day in the life of a SOSUS array
Authors: Rovero P. J. , Miller Christopher W. , Lashkari Khosrow
Published: October 2005

Twenty seven hours of acoustic data from the Point Sur SOSUS array were recorded and analyzed to determine the characteristics of diverse underwater acoustic sources. The SNR and variability of moored RAFOS sources at ranges of 150–1000 km were estimated, as was the source level of imploding incandescent light bulbs. The measured and modeled transmission loss from the bulbs were compared out to the first convergence zone. Finally, the distribution of whale calls in both time and azimuth was determined. These projects are meant to be illustrative of potential uses of Navy array data for both scientific research and graduate education. [Work supported by the United States Navy, Naval Postgraduate School, and Monterey Bay Aquarium Research Institute.]
The new age of scientific partnerships: Acoustic capabilities and facilities at NUWC
Authors: Herstein Peter D. , Monti Joseph M. , Browning David G.
Published: October 2005

In an age of shrinking budgets and the requirement that proposals identify the complete program evolution from scientific concept to manufactured product, partnerships are being encouraged to both share and leverage existing capabilities and facilities. This paper summarizes the acoustic expertise and support services available at NUWC and identifies possible ways of cooperation with other interested parties to develop new products while encouraging basic research in underwater acoustics.
Comparisons of ridge crest earthquake waveforms recorded on SOSUS hydrophones with ocean bottom seismometers in the near field
Authors: Schreiner Anthony E. , Fox Christopher G.
Published: October 2005

The U.S. Navy’s SOSUS network of hydrophone arrays is allowing an unprecedented continuous look at oceanic seismicity. Hydrophones in the SOFAR channel are sensitive detectors of acoustic T-waves resulting from earthquakes in the ocean crust. Since Fall of 1991 a program at the NOAA Pacific Marine Environmental Laboratory has catalogued over 500 seismic events originating on the boundaries of the Pacific, Gorda, and Juan de Fuca tectonic plates. Though extremely sensitive, observations through SOFAR hydrophones have the drawback that the earthquake signal travels long distances though the ocean sound channel. The recorded signal is thus a highly distorted representation of the earthquake. There is as yet no reliably determined relationship between T-wave strength and source magnitude, mainly because many local factors can affect the transfer of energy from the ocean floor into the SOFAR waveguide. We have compared earthquake and explosive events recorded in 1991 simultaneously by the SOSUS network and three small-scale arrays of ocean bottom seismographs placed near the intersection of the Gorda spreading ridge and the Blanco Transform Fault. By this effort, we are attempting to gather enough statistics on long range T-wave strength compared to local measurements to provide a rough magnitude scale.
Wavespace resolution in ultrasonic backscatter measurements
Authors: Mast T. Douglas , Waag Robert C.
Published: October 2005

Pulse-echo measurements of ultrasonic scattering are a useful technique for characterization of scatterer properties, since the spectra of a scatterer’s spatial properties can be determined from the frequency-dependent backscatter coefficient. In such measurements, the spatial localization associated with transducer beam patterns and time gates causes an uncertainty in the measured spatial-frequency domain properties of the scatterer. This uncertainty is analyzed using an analytic and computational model for measurement system effects in backscatter measurements. The results indicate that wavespace resolution is limited in the direction of the scattering vector by the finite durations of the transmitted pulse and the detector time gate, being approximately proportional to the time gate durations. Resolution in the lateral direction depends mainly on the transducer aperture, increasing approximately in proportion to the aperture diameter. Smooth aperture apodization improves lateral resolution somewhat but has little effect on resolution in the direction of the scattering vector.
New acoustical approaches to perfusion and other vascular dynamics
Authors: Fowlkes J. B. , Ivey J. A. , Gardner E. A. , Rubin J. M. , Carson P. L.
Published: October 2005

Manipulation of bubble-based ultrasound contrast has been examined for the purpose of perfusion measurement. By exposing a dialysis tube (0.6 cm diam) of flowing blood (20 to 50 ml/min) containing albumin-stabilized contrast agent to a burst of a 0.75-MHz field at 0.2 MPa, the additional Doppler and b mode signal produced by the microbubbles was interrupted and then increased beyond the initial level. The experiment was also performed using a constant infusion of contrast agent into the blood flow and a much lower amplitude acoustic field (0.05 MPa) was able to start and stop the flow of bubbles. Similar control over bubble flow was observed in a kidney perfusion phantom where a standard colored microsphere technique indicated that the washin–washout time for the contrast scaled linearly with perfusion. Finally an experimental system has been developed which generates a contrast bolus invivo without the introduction of stabilized microbubbles. The bolus generated by this system in the descending aorta of the dog using was visible in a distal artery of the leg. Therefore it may be possible to make perfusion and vascular flow measurements without the addition of stabilized contrast agents.
How accurate are volume flow measurements using Doppler ultrasound from commercial systems?
Authors: Winkler Andrew J. , Wu Junru
Published: October 2005

The accuracy of volume flow measurements using Doppler ultrasound was tested on a calibrated volume flow phantom for several commercial systems (ATL Ultramark4 and Ultramark9, Hewlett-Packard Sonos 1000, Quantum Quad1 and Acuson 128). The phantom consists of a plastic tubing (inner diameter: 0.64 cm) running through a rectangular plastic container filled with gelatin-based tissue-mimicking material. Solutions of glycerol, water, and cellulose powder mixture, whose viscosity was 5 cp at 25 °C, were circulated through the tubing with a variable speed roller pump. The preliminary results showed that the volume flow measured by the above-mentioned commercial systems were overestimated by 25%–50%.
The acoustic field of a pulsed Doppler diagnostic ultrasound system near a pressure-release surface
Authors: Holland Christy K. , Sandstrom Kurt , Zheng Xiaoyu , Rodriguey Jed , Roy Ronald A.
Published: October 2005

Extravasation of blood cells has been observed in the lungs of mice and monkeys exposed to pulsed ultrasound conditions comparable to diagnostic levels [Child etal., Ultrasound Med. Biol. 16, 817–825 (1990) and A. F. Tarantal and D. R. Canfield, Ultrasound Med. Biol. (in press)]. In order to understand the ultrasound exposure conditions under which damage occurs, lung was modeled as a simple interface from water to air. The acoustic pressure output of an Advanced Technology Laboratories Ultramark 9 High Definition ImagingR system with a 5-MHz linear array transducer in pulsed Doppler mode (4 MHz) was interrogated near the pressure release surface (≤3 mm) with a Marconi 0.5-mm bilaminar membrane-type PVDF hydrophone. For the nonlinear waveforms produced, peak negative pressures of 2.0 MPa measured in free filed were increased to 4.5 MPa due to constructive interference near the interface. The behavior of the pressure release surface was also simulated computationally as a low-pass filter with a 180° phase shift. The impulse response of the interface was constructed using experimentally measured spectra of the incoming and reflected waves. The pressure waveform was calculated as a function of position by superimposing the incoming and reflected waves and was compared to the hydrophone measurements. The implications of these observations on insitu acoustic exposure near lung will be discussed.
Thresholds for transient cavitation produced in phantoms by pulsed megahertz frequency ultrasound at various pulse conditions
Authors: Zheng Xiaoyu , Xu Qihong , Apfel Robert E.
Published: October 2005

The purpose of this work is to provide measurements in well characterized media in order to better understand transient cavitation phenomena and eventually to study cavitation-induced, invivo bioeffects. In order to investigate the potential for transient cavitation generated by pulsed megahertz frequency ultrasound, a modified ‘‘active detection’’ system [Roy etal., J. Acoust. Soc. Am. 87, 2451–2458 (1990)] has been used. Highly focused transducers with megahertz center frequencies were used as driving transducers to cause cavitation. Experiments were first conducted in distilled water with polystyrene particles serving as nuclei for cavitation sites. Transient cavitation thresholds were measured for various nuclei concentrations and different sizes of nuclei. Measurements of the cavitation thresholds were then made in some tissue-mimicking (TM) phantom materials that are specially developed to exhibit attenuation coefficients similar to soft tissues. The dependence of the transient cavitation threshold on pulse characteristics (duty cycle, pulse length, pulse repetition frequency) were also investigated. [Work supported by NIH through Grant. No. R01 CA39374.]
Active cavitation detection of microbubble echocontrast agents in blood
Authors: Huertas Vilma E. , Makin Inder Raj S. , Everbach E. Carr
Published: October 2005

Apfel’s active cavitation detector [Roy etal., J. Acoust. Soc. Am. 87, 2451–2458 (1990)] has been improved to allow quantification of microbubble activity in reconstituted human blood. One-microsecond-long 20-MHz tone bursts are scattered from microbubbles undergoing transient cavitation at the focus of a pulsed 1-MHz transducer. The host medium consists either of human red blood cells suspended in autologous plasma or platelet-rich plasma, with various concentrations of microbubble-based echocontrast agent present. The microbubble activity inferred from the backscattered tone bursts is compared to measured bioeffects (hemolysis, platelet aggregation) in order to determine the physical basis for cavitational damage of blood components. Current results as a function of system parameters will be presented. [Work supported by NSF MSS-9253777.]
Cavitation from short pulses of megahertz-frequency ultrasound
Authors: Calabrese Adam , Allen John , Roy Ronald A.
Published: October 2005

Recent studies have demonstrated that cavitation can be produced by short pulses of megahertz-frequency ultrasound. These studies employed a detection scheme that keyed only on the onset of detectable cavitation. Cavitation thresholds measured using this approach do not accurately reflect nuclei statistics, for one is concerned only with the pressure required to activate the ‘‘weakest’’ nuclei. Moreover, this technique offers little information regarding cavitation production rates, which are likely to be better correlated to a mechanical bioeffect than the threshold alone. In the present study, a passive cavitation detector [Roy etal., J. Acoust. Soc. Am. 87, 2451–2458 (1990)] us used to estimate the rate of cavitation production as a function of acoustic pressure amplitude. This measurement is repeated for a variety of insonating pulse lengths and duty cycles and at frequencies of 1 and 2.25 MHz. Results suggest that the threshold pressure for cavitation is weakly dependent on pulse length, and decreases with increasing duty cycle. In addition, cavitation production rates appear better correlated to duty cycle than pulse length. [Work supported by NIH.]
Temperature distribution and noninvasive monitoring during ultrasonic hyperthermia
Authors: Ding Ying , Fan Hua , Wang Hong-Zhang
Published: October 2005

In the ultrasonic hyperthermia for cancer therapy, for keeping the heating temperature in a certain range and avoiding problems from needle insertion, noninvasive monitoring of temperature is needed and has been developed. Using the bioheat transfer equation including thermal source, the temperature distribution at times has been calculated by the finite element method under certain boundary conditions. The influence of the focusing, tumor size, blood perfusion, and temperature of skin, etc., on the temperature field inside the human body, has been investigated. It is found that good control of the power emission can be made by measuring the skin surface temperature which has a definite relation with that at the focus under a certain group of parameters. It has also been found that the temperature at the equilibrium state due to the balance between sound power deposition and heat diffusion by blood perfusion can be calculated. This law can also be used to control the ultrasonic power emission for hyperthermia. The change of the temperature distribution corresponding to a change in the depth of focus has been investigated in detail. This can help to make the effective heating area enough to cover the whole cancer, so as to improve the efficacy of the therapy.
The evolution of sonar transducer technology on U. S. surface ship and submarine platforms
Authors: McTaggart Bernard E.
Published: October 2005

This paper will discuss the evolution of sonar transducer design from the first World War to the present. Submarines and surface ships had basically no sonar equipment to track adversaries in the first World War yet from that period to the present, tremendous advances have been made in the development of both transduction concepts and materials. This paper will address the evolution of echo ranging and passive ranging systems, intercept receivers and depth sounders, and how today’s sophisticated equipment evolved from the crude technology of the first World War. Rather than discussing systems performance, electronics, and signal processing, emphasis will be placed on transducers, hydrophones, and materials.
Loss processes in piezoelectric PVDF and their effect on broadband transducers
Authors: Summa D. A. , Hixson E. L.
Published: October 2005

Classic electromechanical models are extended to transducers fabricated from inherently lossy polymeric materials. To augment sparse data, phenomenological models and molecular estimation techniques based upon structure-property relationships are used to examine relaxation processes and reconstruct elastic and dielectric loss tangent surfaces as a function of frequency, temperature, and pressure (f,T,P). The improved material descriptions are used to assess the acoustic performance of a typical thickness-mode PVDF hydrophone over a range of environmental parameters of interest in sonar. Variations in elastic parameters shift the resonance frequency, cause a departure from a truly ‘‘ρc-matched’’ condition, and introduce a dynamic variation in the open-circuit receive sensitivty. Variations in the dielectric parameters of similar magnitude occurring at the same (f,T,P) coordinates ensure that the wideband response remains flat to within 1 dB, depending upon the geometry of the device and operating parameters chosen. The effects of intrinsic material losses are most pronounced in the internal noise spectrum of the PVDF hydrophone. In warm waters noise levels average 10 dB lower than predicted by a constant loss model, whereas in cool waters noise levels are 6–10 dB below the predictions based upon these models at low frequencies [O(102) Hz], rising to 10–18 dB above the constant loss predictions at frequencies on the order of 104–105 Hz. [Partial support provided by the Independent Research & Development Program, Applied Research Laboratories, The University of Texas at Austin, Austin, TX.]
Piezoelectric composite transducers
Authors: Bowen Leslie , Gentilman Richard , Pham Hong , Fiore Daniel
Published: October 2005

Piezoelectric ceramic/polymer composites have found increasing use in high resolution medical ultrasound systems and advanced Navy underwater acoustic applications. Composite transducers offer design versatility and performance advantages over monolithic piezoelectric ceramic and monolithic piezoelectric polymer devices under both sensing and actuating conditions. In particular, composite transducers allow improved acoustic impedance matching to water and body fluids, improved lateral mode cancellation, enhanced thickness mode coupling coefficient, and naturally broad bandwidth. However, applications for these versatile transducers have been limited by the difficulties of cost-effectively manufacturing the arrays of fine PZT ceramic elements required for composite assembly. At Materials Systems, Inc., ceramic injection molding has been developed into a viable net-shape process for making complex-shaped, fine scale PZT 1-3 and 2-2 transducer element arrays. This presentation describes the injection molding approach for manufacturing piezocomposite transducers, and reviews the sensing and actuating performance of injection molded 1-3 transducers over the frequency range 1 kHz to 5 MHz. [This work is funded by ONR.]
Acoustic and aerodynamic determinants of the sound quality of flutes
Authors: Fletcher Neville H.
Published: October 2005

After nearly 200 years of research, the precise nature of the aerodynamic driving mechanism of flutes and organ pipes is still incompletely determined. First-order theories using simplified acoustic approximations give reasonable agreement with experiment in terms of the dependence of acoustic output power and spectrum on the parameters available to the instrument maker and the player, but a detailed description needs to take account of aerodynamic phenomena at the level of individual vortices. A current version of the theory is presented and discussed in relation to the control of sound quality available to the flute player through selection of embouchure-hole size and shape and by variation of playing technique. New measurements on some of these quantities are presented.
Order and disorder in ribbed membranes with fluid loading
Authors: Spivack Mark , Barbone Paul E.
Published: October 2005

The response to harmonic forcing both of regularly and of irregularly ribbed fluid-loaded membranes has been studied under the assumption of subsonic wave coupling. The solution for any given rib configuration is obtained exactly in terms of 2×2 transfer matrices. In the irregular case it is well known that localization occurs at all driving frequencies; nevertheless there are distinct regimes of smooth and fluctuating decay. These are shown to be closely related to the stop- and passbands found in regularly supported membranes, and this is explained in terms of the characteristics of the transfer matrices. This approach can be generalized to any problem in which the long-range behavior of the Green’s function is the same as for the case of subsonic wave coupling. [Work supported by Smith Institute Research Fellowship and ONR.]
Wave-based theory of sound scattering by a periodically ribbed submerged cylindrical elastic shell
Authors: Felsen Leopold B. , Shaya Ronald
Published: October 2005

A previous angular harmonic series analysis of scattering from a periodically ribbed submerged elastic infinite cylindrical thin shell [C. B. Burroughs, J. Acoust. Soc. Am. 75, 715–722 (1984)] is converted into a wave-based analysis that emphasizes circumferential wave phenomena in the scattering process. The conversion is accomplished by extending the azimuthal mode index from its periodicity-constrained integer values n to a ν continuum in periodic infinite angular domain. Subject to the n→ν replacement, the Burroughs solution furnishes the integrand in the (ν,β) spectral wave-number domain that corresponds to the (φ,z) angular-axial space coordinates. The analytic properties of the spectral integrand, which is separated into bare-shell and angular-rib-induced scatterings, are examined, and the (ν,β) spectral synthesis is performed in a manner that favors extraction of ray-acoustic phenomenology by high-frequency asymptotics. The asymptotic reduction of this ray-acoustically parametrized solution for the acoustic pressure, which is exact except for thin shell asymptotics, is performed in the companion paper [L. B. Felsen and R. Shaya, following paper].
The effects of fuzzy attachments on compressional and shear waves in a plate
Authors: Rochat Judith L. , Sparrow Victor W.
Published: October 2005

Using the theory established by A. D. Pierce etal. [ASME Paper 93-WA/NCA-17 (1993)], regarding fundamental structural-acoustic idealizations for structures with fuzzy internals, the effects of fuzzy structures on different wave types are examined. In this problem, the structure that undergoes vibrations is a rectangular elastic plate mounted in an infinite baffle. On one side of the plate is a fuzzy structure, represented as a random array of point-attached spring-mass systems. The known theory explains the effect of these attachments on bending waves in the plate. In this presentation, the theory is extended to isolated compressional and shear waves and predicts that, in either case, the fuzzy structure can be modeled in the system solely by (1) an added frequency-dependent mass and (2) an added frequency-dependent damping. These results are similar to those for bending waves. [Work supported by ONR.]
Speech production models in automatic speech recognition—Forming a lasting marriage between speech science and speech technology
Authors: Rose R. C. , Schroeter J. , Sondhi M. M. , Ghitza O.
Published: October 2005

At present, the performance of automatic speech recognition (ASR) systems is still limited by variabilities within and between speakers, by acoustic differences between training and application environments, and by the sensitivity of ASR systems against changing communication channels. This talk considers the conjecture that the use of speech-production models in ASR systems can contribute to making ASR systems more robust with respect to these sources of variability. Although it is well known that production-oriented representations of speech may be used to exploit the continuity of articulatory movements, several obstacles stand in the way of incorporating speech production models in recognizers. These include the difficult problem of acoustic-to-articulatory mapping, the hugh complexity of searching an articulatory space, and the lack of sensitive diagnostic performance metrics for evaluating strengths and weaknesses of a particular production model. Several research laboratories are actively involved in efforts towards incorporating articulatory models in various forms in working ASR systems. In addition to summarizing this work, mechanisms will be suggested for stimulating closer interaction between researchers in production, perception, and processing.
Speech perception is hearing sounds, not tongues
Authors: Ohala John J.
Published: October 2005

Should the human or mechanical listener attempt to recover articulatory information when recognizing speech? The answer is ‘‘no,’’ with one qualification: listeners who need eventually to speak out loud the utterances they hear others make would be aided by figuring out what other speakers do with their vocal tracts but even in this case it may not be absolutely necessary. (There is also no dispute that the speech scientist wishing to understand how speech works needs to known the articulations giving rise to specific sounds.) The argument has three parts: (a) the phonologies of languages (e.g., their segment inventories, phonotactic patterns, etc.) unmistakably optimize sounds, not articulations; (b) infants and even various nonhuman species can differentiate certain sound contrasts in human speech even though it is highly unlikely that they can deduce vocal tract movements generating the sounds; (c) humans can differentiate many nonspeech sounds almost as complex as speech, e.g., music, machine noises, as well as bird and monkey vocalizations, where there is little or no possibility of recovering the mechanisms producing the sounds.
Ocean variability, modal group delays, and the detection of climate signals with vertical arrays
Authors: Baggeroer Arthur B.
Published: October 2005

The monitoring of ocean variability and climate using global acoustics depends upon detecting travel time changes of the resolvable modes and/or raypaths. An analysis based upon the modal group delays is considered. It is assumed that they contain the information that acoustic probes can yield about an adiabatic ocean; consequently, a water column-spanning vertical line array that measures all group delays can extract all the information about ocean variability and climate that acoustics can provide. The vertical slice is modeled along the path with two components: (i) a set of possible climate signals, e.g., warming at the surface or at the SOFAR duct and (ii) a natural variability based upon the ocean dynamical modes. Noise is included in the measurements of the delays due to acoustic signal-to-noise ratios, finite bandwidths, and array imperfections. Then the covariance of the modal group delays due to natural variability is found and estimation theory bounds are evaluated on how well the climate signals can be estimated using vertical line arrays to measure the group delays. [Work supported by ARPA.]
Assimilation of acoustic data into oceanographic models
Authors: Kuperman W. A. , Porter M. B. , Shen C.
Published: October 2005

The acoustic thermometry of the ocean (ATOC) program involves the use of global acoustic paths to sample the ocean climate. Ultimately, ocean and acoustic model and data must be integrated to produce reliable estimates of climate scale oceanographic phenomena. Here, through simulation, a scaled down model of acoustic data assimilation for oceanographic purposes is studied. A thousand kilometer square ‘‘real’’ model ocean that varies temporally and spatially is probed acoustically and the data are assimilated into an appropriate oceanographic model. A methodology of updating the oceanographic model with acoustic data to track the ‘‘real’’ ocean is discussed. The technique is based on combining a nonlinear optimization version of matched-field tomography with an optimal interpolation assimilation algorithm linked to an oceanographic model.
Use of Naval facilities for ocean acoustic research
Authors: Mosier Mary P.
Published: October 2005

The United States Navy’s oceanographic system was established in 1954 with the commissioning of Naval Facility Ramey. Established as the United States’ first line of defense against submarines, the oceanographic systems has grown into the integrated underseas surveillance system (IUSS). IUSS is comprised of two parts. The fixed system is called the sound surveillance system or SOSUS and the mobile system is called surveillance towed array sensor system or SURTASS. Since the end of the cold war and the declassification of its antisubmarine warfare mission, IUSS has made acoustic data available to other government agencies and the scientific community on a case-by-case basis. Present and potential research areas using IUSS acoustic data include large marine mammals, acoustic telemetry, remote ocean observation, fisheries enforcement, and seismic/volcanic monitoring. Limitations to the availability of this data is classification of sensor locations and signal processing technology, compatible equipment, financial impact on the United States Navy and impact on primary mission at the facility. This presentation will provide you with the key to working with IUSS facilities.
NOAA’s use of U.S. Navy fixed hydrophone arrays for monitoring the Juan de Fuca Ridge
Authors: Fox Christopher G.
Published: October 2005

NOAA’s VENTS Program studies the impact of seafloor hydrothermal emissions on the chemical and thermal budgets of the global ocean. The research focus has been on seafloor spreading centers, in particular the Juan de Fuca Ridge in the northeast Pacific Ocean, and early results indicated the episodic nature of activity. Since no method existed for long-range continuous monitoring, NOAA obtained permission to collect acoustic data from U.S. Navy’s sound surveillance system (SOSUS) in the north Pacific Ocean. Two NOAA systems have been installed to process the signals independently and in parallel with the Navy’s operational systems. One system uses outputs from two end hydrophones from five arrays to analyze seismicity through the north Pacific. The second system collects outputs from formed beams directed at the Juan de Fuca Ridge for real-time monitoring. An acoustic beacon (260 Hz), installed on a seamount, allows continuous monitoring of travel times for location correction. Use of the SOSUS system produces an increase in the number of earthquake detections from ∼350 events/year to ∼7500 events/year for the northeast Pacific. In 6 months of operation, the real-time monitoring system has detected two episodes of volcanic activity, later documented by field observations.
Ocean weather and climate observations using the IUSS
Authors: Mercer James A.
Published: October 2005

For more than a decade, long-range acoustic propagation measurements have been used to remotely infer characteristics of the oceans’ interior structure. The most prominent efforts have been those focused on the application of tomographic methods to measure the sound speed and current fields, and by inference the temperature field. To a large degree, the genesis of this activity was earlier measurements taken on the U.S. Navy’s undersea surveillance system, and IUSS remains a central part of many experiments being conducted today. This paper will illustrate the importance of the Navy’s assets to several recent experiments and will highlight the role of IUSS in the multi-institutional Acoustic Thermometry of Ocean Climate (ATOC) Program. [Work supported by ONR and ARPA.]
Interaction between response modulation and adaptation in the auditory nerve
Authors: Smith Robert L. , Nguyen My
Published: October 2005

Dynamic response properties of single auditory-nerve fibers and the corresponding modulation following response (MFR) at the round window were obtained in anesthetized Mongolian gerbils. Stimuli consisted of adapting tones followed, after a silent interval, by probe tones. Both tones were amplitude-modulated by sinusoids, and the modulating waveforms were applied first in one phase, then 180 deg out of phase. Responses to the two phases of modulation were combined in order to generate sum and difference waveforms. For the single-unit responses, this allowed computation of both adapting firing rates (from the sum) and response modulation (from the difference) as function of time, while only the latter were obtained for the MFR. When the intensity of the adapting and probe tones were varied, it was observed that the single-unit response modulation varied in proportion to the underlying firing rate for both adapting and probe responses. In addition, the amount of adaptation varied in proportion to the steady-state firing rate, in agreement with previous results. A similar proportionality was observed for the MFR, consistent with the hypothesis that the MFR provides a convenient indirect measure of the ongoing firing rate during adaptation of auditory nerve-fiber responses. [Work sponsored by NIH and NSF.]
Effects of complex-sound phase in the chinchilla auditory nerve
Authors: Narayan S. Shyamla , Chen Guang-Di
Published: October 2005

Responses of populations of single auditory nerve fibers in anesthetized chinchillas to three-component stimuli were studied. The carrier frequency ( fc) was 2 kHz and the modulating frequencies ( fm) were 100 and 1000 Hz. The sidebands were −6 dB relative to the center component. The phase of the center component was varied from 0 to 180° in 45° steps, which produced changes in modulation depth. Discharge synchrony to fm=100 Hz decreased with increasing stimulus level for CFs close to fc, as previously shown by other researchers. At 20 dB re:unit threshold, maximum synchrony to 100 Hz was observed for CFs close to fc. The maxima shifted to higher CFs with increase in stimulus level. Synchrony to fc decreased with phase shifts up to 90° and increased for phase shifts between 90° and 180°. At 20 dB, synchrony to the lower sideband was less than that to the upper sideband when the phase shift was 90° and 135°. At 40 dB, 0° and 180° phase shifts produced higher discharge synchrony to the lower sideband. Also at 40 dB, the phase dependence of the synchrony to the two sidebands differed most at the lower CF regions. The changes in discharge synchrony due to phase changes must reflect cochlear nonlinearities because the amplitude ratios of the stimulus components were held constant. [Work supported by DC00341.]
Mechanisms involved in the phase sensitivity of auditory nerve fibers in the bullfrog
Authors: Bodnar Deana A. , Capranica Robert R.
Published: October 2005

Auditory nerve fibers in the bullfrog (R. catesbeiana) are sensitive to shifts in the phase spectra of complex sound stimuli. Fibers innervating both auditory organs, the amphibian papilla (AP) and basilar papilla (BP), exhibit changes in their synchronization to the fundamental period of a multi-harmonic stimulus with shifts in its phase spectrum. In addition, AP fibers also exhibit changes in their firing rates. To determine whether these changes actually reflect sensitivity to the peak amplitude of a stimulus waveform, the changes in spike rates and synchronization characteristics of AP and BP fibers were compared with the waveform’s peak amplitude. In BP fibers, synchronization to the fundamental period is highly correlated with changes in the stimulus waveform’s peak amplitude. However, changes in the waveform’s peak amplitude cannot account for changes in the spike outputs of most AP fibers. Therefore, additional mechanisms must be involved in the phase sensitivity of AP fibers. Suppression and distortion nonlinearities contribute to the phase sensitivity of some low-frequency AP fibers, but cannot explain the phase sensitivity observed in all AP fibers. Other micromechanical interactions and/or sensitivity to the fine-temporal structure of the stimulus waveform may play a role. [Work supported by NIH.]
Developmental changes in auditory nuclei of the torus semicircularis in the American bullfrog (Rana catesbeiana)
Authors: Boatright-Horowitz S. , Simmons A. M.
Published: October 2005

Anuran amphibians undergo significant neural remodeling of their auditory system as they progress from aquatic larvae to semi-terrestrial adults. It has previously been shown that post-metamorphic auditory maturation in bullfrogs shows great similarity to the typical vertebrate postnatal developmental pattern of decreasing maximally sensitive frequency and sharpening of tuning until achieving the u-shaped audiogram of the adult. These changes in neural response properties are accompanied by morphological changes in auditory nuclei in the midbrain. Histological examination of brain sections reveal physical changes in the auditory midbrain of frogs across postmetamorphic development. The midbrain increased in size significantly from a 1-day post-metamorphic froglet (3.1 cm SVL) to an adult (16.1 cm SVL), with most of the increase due to lateral hypermorphosis in the region containing the torus semicircularis, a homologue of the mammalian inferior colliculus. The expansion of the torus is not due to postmetamorphic cellular division, as the cell body density decreases across development. Tracing studies also reveal changes in connectivity patterns across development. These data suggest that there may be discrete developmental stages in the maturation of the bullfrog’s central auditory system. [Work supported by NIH and NSF.]
Transient changes in neural discharge patterns may enhance the separation of concurrent vowels with different fundamental frequencies
Authors: Cariani Peter , Delgutte Bertrand
Published: October 2005

Two vowels presented concurrently are better identified by human listeners when their fundamentals (F0’s) differ. Neurophysiological correlates of this phenomenon were investigated using single fiber recordings from the auditory nerve of anesthetized cats. Results show that aggregate interspike interval distributions (the summed autocorrelation histograms of many fibers with different CF’s) contain sufficient information to characterize single vowels. When two concurrent vowels have the same F0, the resulting interval distributions resemble that of one ‘‘dominant’’ vowel constituent. When the two vowels have different F0’s, running interval distributions additionally show short time segments when they resemble the other, ‘‘nondominant’’ vowel. These short time segments and accompanying changes in interval distributions are associated with shifting relative onset times of vowel periods (i.e., changes in vowel period alignments) created by the different F0’s. Particular period alignments can enhance or diminish the similarity of the interval distribution with that of either vowel constituent. These results along with recent psychophysical findings [P. Assmann and Q. Summerfield, J. Acoust. Soc. Am. 95, 471–484 (1994)] suggest that differences in F0 may allow the auditory system to ‘‘hear out’’ each vowel in moments when period alignments are favorable. [Work supported by NIH DC00119.]
Interval statistics generated from a cochlear model in response to speech sounds
Authors: Sheikhzadeh H. , Deng L.
Published: October 2005

In this paper temporal aspects of auditory representation for several classes of speech sounds are studied. A modeling approach is taken in which a composite auditory model is used to generate paralleled sets of PST histograms along the spatial dimension, followed by a processing stage that constructs from the PSTHs the interval statistics in a form called inter-peak interval histogram (IPIH). Given the PSTH data from the auditory nerves in response to the identical speech stimuli, the goodness of fit between the computer-simulated IPIHs and the neural IPIHs is usable as a criterion to investigate the functional significance of the cochlear model’s parameters. In particular, it was found that no satisfactory neural match can be obtained when the parameters controlling the bandwidths and the nonlinear damping elements of the basilar-membrane filters are set inappropriately. Using the ‘‘optimally’’ tuned model parameters according to the neural-matching criterion, sequences of IPIHs were generated from the auditory model’s response to natural utterances (TIMIT) encompassing all major manner classes of American English: vowel, diphthong, semivowel, nasal, fricative, stop, and aspiration. Analysis of the results allows one to clearly identify major acoustic properties of the utterances from the simulated IPIHs. Further, when the IPIHs are constructed from the auditory model’s response to noisy version of the utterances, it is observed that the original acoustic cues are affected little by the noise level.
Temporal bandpass filters from simulated cochlear nucleus neurons
Authors: Krieger Josh
Published: October 2005

A bank of temporal bandpass filters was simulated using model cochlear nucleus neurons. Average firing rate equations were used to model chopper neurons as slow average rate integrators (lowpass filters with low cut-off frequencies) and primarylike neurons as fast average rate integrators (lowpass filters with high cut-off frequencies). Using the principle that the difference of two lowpass filters is a bandpass filter, the filter bank was constructed so that the output at a particular point was the difference in output rates of a primarylike and a chopper neuron at that same point. Different bandpass shapes were generated by varying model neuron parameters. In the linear case, only three parameters for each chopper/primarylike pair are needed to completely specify a simple closed-form solution for the bandwidth and center frequency of the temporal filter. [Frisina etal., Hear. Res. 44, 99–122 (1990)] described bandpass filterlike responses from a spectral analysis of single unit PSTH recordings in cochlear nucleus. An explanation of this phenomena in terms of saturation neuron firing rates was given by [Hewitt etal., J. Acoust. Soc. Am. 91, 2096–2109 (1991)]. The model presented here relies on a fundamentally different scheme for generating bandpass filter.
Temporal process model for periodicity extraction in frog auditory system
Authors: Shen Y. , Sanderson M. , Simmons A. M.
Published: October 2005

One simple time-domain demodulation model, equipped primarily with (1) a bandpass filter, (2) a nonlinear rectifier, and (3) a lowpass filter, has been contrived to test the suggestion that frog auditory nerve fibers encode periodicity by a temporal mechanism, rather than by a rate-place mechanism, as strongly indicated from physiological experiments [A. M. Simmons and M. Ferragamo, J. Comp. Physiol. 172, 57–69 (1993); A. M. Simmons etal., J. Acoust. Soc. Am. 93, 3374–3389 (1993)]. With one set of model parameters, this model can quantitatively replicate up to 80% of the periodicity extraction observed in all fibers stimulated with complex sounds. The sensitivity of the model to phase information has been examined through driving it with seven frequency-component stimuli with different phase combinations. Different intensities (+10, +20, and +30 dB above threshold) are employed to test the effect of nonlinear gain control and saturation on dynamic range. Extensive numerical simulation has been used to identify the optimal parameter set to maximally match model response with experimental results. Partitioning of fibers into different CF groups provided further insight between model parameters and physiological data. A short-term adaptation unit has been added to the model and tested with experimental data as well. [Work supported by NIH.]
A delay-cell network for pitch estimation
Authors: Mountain David C.
Published: October 2005

Autocorrelation functions have played a prominent role in many theories of pitch perception. A problem with relating such theories to a physiological substrate is that the autocorrelation function must be computed for delays as large as 5–20 ms which is much longer than what would be expected from conduction or synaptic delays. The delay-cell network [D. C. Mountain, ARO Abstracts 16, 107 (1993)] implements these delays via the combination of a fast-acting inhibitory input and a slower-acting excitatory input synapsing on the same cell (delay cell). The output from a layer of these delay cells (each with different delay) is then fed to an output layer consisting of coincidence detectors. This layer compares the delayed versions of the signal to the undelayed signal. The representation produced by the network is a smoothed interval histogram rather than an autocorrelation function. Simulations of the delay-cell network predict that it should be possible to elicit pitch percepts using click trains with a random interclick interval. Preliminary experiments indicate that these random click trains do elicit a pitch sensation which varies with the mean interclick interval. The autocorrelation functions for such stimuli are quite broad and exhibit no clear peaks. [Work supported by ONR.]