bluuebunny/crossref_metadata_2025 huggingface dataset:
Range dependence in the level set method for underwater acoustics.
Authors: Martinelli Sheri L.
Published: March 2010

The level set method due to Osher and Sethian [J. Comput. Phys. 79, 12–49 (1988)] provides a way to obtain fixed grid solutions to the high-frequency wave equation. Instead of tracing rays from the source, the level set method embeds the wavefront implicitly in the phase space and propagates it according to the velocity field determined by the local ray direction, thus avoiding the complications involved in the spatial reconstruction of wavefronts from diverging rays. A level set method has been developed and implemented as a fixed-grid alternative to ray tracing to solve for the acoustic phase. One of the issues that arises with the increased dimensionality of posing the propagation problem in the level set framework is that the presence of reflecting boundaries produces a discontinuity in the phase space corresponding to a sudden change in propagation direction. When a reflecting boundary is range-dependent, further complications arise. To improve algorithm performance, specialized methods are applied to the level set equations that combine upwinding with higher-order spatial interpolation that avoid the generation of spurious oscillations that occur with most traditional finite difference methods. [Work supported by ONR 333 and the SMART Program.]
An algorithm to predict surface loss.
Authors: Clark Cathy Ann
Published: March 2010

A semi-empirical surface loss algorithm is presented which is comprised of a rough scattering component derived from theory and a term which represents low-frequency, low angle loss from other mechanisms such as absorption and bubbles, based on a fit to measured data. A prediction of surface duct propagation using the semi-empirical algorithm and a current Navy standard propagation model is compared to measured data.
Boundary flattening transforms for acoustic propagation under rough and periodic sea surfaces.
Authors: Oba Roger
Published: March 2010

A conformal transform is presented that maps an acoustic domain with a one-dimensional, rough sea surface onto a domain with a flat top. The non-perturbative transform presented here broadly generalizes that of Dozier [J. Acoust. Soc. Am. 75, 1415–1432] to include many wavelengths of the surface variation. A two-dimensional, flat-top domain permits the direct application of a parabolic equation model acoustic propagation model for the Helmholtz equation using a modified sound speed. Once the field is computed, the inverse transform permits the acoustic field interpolation in terms of the original coordinates. The mapping is derived from techniques in the classical theory of flow around an airfoil. Forward scatter test cases with periodic and rough sea surfaces provide verification of the method using a parabolic equation model. The periodic surface case demonstrates scattering from steep grazing angles to shallower ones. An extension to scattering to irregular cylinders is outlined following the scheme of DiPerna and Stanton [J. Acoust. Soc. Am. 96, 3064–3076, (1995)]. [This research is sponsored by the Office of Naval Research.]
Horizontal Lloyd mirrors arising from propagation through straight and curved nonlinear internal wave fronts.
Authors: McMahon Kara G. , Reilly-Raska Laurel K. , Lynch James F. , Duda Timothy F. , Siegmann William, L.
Published: March 2010

Experimental observations and theoretical studies show that nonlinear internal waves (NIWs) occur widely in shallow water and cause acoustic propagation effects including mode coupling and ducting. Horizontal ducting results when acoustic modes interact with NIW fronts that comprise waveguide boundaries. For small grazing angles between a mode trajectory and a front, an interference pattern may arise that is hypothesized [Lynch et al., J. Ocean Eng. 31, 33–48 (2006)] to be a horizontal Lloyd mirror. We examine acoustic formulations for this feature and benchmark calculations for the acoustic intensity with those from the adiabatic mode parabolic equation. Results using different waveguide features are compared, including continuous-gradient and jump sound-speed profiles of varying strengths. We focus on differences in the location of the source relative to the NIW as well as the frontal curvature. The curvature influences both incidence angles and reflection characteristics. For sources oriented inside the front, as curvature increases the areas with interference patterns shrink, while sources beyond the front cause patterns to expand. [Work supported by ONR.]
Blind deconvolution of remote-source signals from ocean acoustic array recordings.
Authors: H. Abadi Shima , R. Dowling David , Rouseff Daniel
Published: March 2010

Reconstructing the signal originally broadcast from a remote source in an unknown multipath environment is a task commonly known as blind deconvolution. At frequencies of several kilohertz and above, multipath shallow-ocean sound propagation may be adequately described by ray acoustics. This presentation describes results from the application of ray-based artificial time reversal (ATR) to underwater sound propagation measurements. The receiving array was vertical and it recorded signals with center frequencies and bandwidths of a few kHz at source-receiver ranges up to 3 km in a water depth of approximately 60 m. Ray-based ATR uses a simple-beam-former-determined ray-arrival direction to construct a frequency-dependent phase correction at the receiving array that allows the Green’s function of the sound channel and the original source waveform to be separately estimated. Here, the correlation coefficient between the original signal and the ATR-reconstructed signal is presented as a function of range and signal-to-noise ratio. In addition, the effect of reducing the number elements of the receiving array and the use of a coherent combination of reconstructed results for various ray arrival directions on cross correlation coefficient will be discussed. [Work supported by ONR.]
Optimal loudspeaker placement for sound field reconstruction in geometrically constrained environments.
Authors: Atkins Joshua , West James
Published: March 2010

The design of loudspeaker arrays for holographic sound reproduction systems involves sampling a given aperture by a set of loudspeakers. For full sphere apertures it can be proven that there are only five equidistant sampling methods (given by the five regular polyhedrons) which only allows for arrays with up to 20 elements. For larger arrays, non-equidistant design methods such as t-design and Gaussian sampling have been proposed. However, in realistic environments it is generally not possible to place loudspeakers on the floor or on walls at certain locations. Furthermore, it is not desirable to have the loudspeakers constrained to spherical radii. This work shows a method for loudspeaker array design that allows for consideration of these special cases. The method relies on the decomposition of the sound field into a spatially orthonormal basis of spherical harmonics. A heuristic method is used to minimize the eigenvalue spread of the spherical harmonic matrix. The loudspeaker weights are found by calculating the generalized inverse of this matrix. Constraints on the speaker positions, highest reproduction mode, and number of loudspeakers are imposed in the minimization. The results of a design for a 16 speaker array in our acoustics laboratory are discussed.
Classification of marine mammal vocalizations using an automatic aural classifier.
Authors: Hines Paul C. , Ward Carolyn M.
Published: March 2010

Passive sonar systems are often used to detect marine mammal vocalizations in order to localize and track them. Unfortunately, transients generated by sources other than marine mammals can also trigger passive sonar systems which leads to a large number of false alarms. Furthermore, even in the case of a successful detection, classifying the genus is often required and this typically requires expertise not readily available on the vessel. Perceptual signal features—similar to those employed in the human auditory system—have been used to reduce false alarms in active sonar by automatically discriminating between target and clutter echoes. This contributes to improved sonar performance [Young and Hines, J. Acoust. Soc. Am. 122, 1502–1517 (2007)]. Many of the features were inspired by research directed at discriminating the timbre of different musical instruments (a passive classification problem) which suggests it might be applied to classify marine mammal vocalizations. To test this hypothesis, the automatic aural classifier was trained and tested on a set of marine mammal vocalizations from a variety of species. This paper will provide an overview of the aural classifier’s architecture, describe the preparation of the data set, including the attempt to provide ground-truth confirmation of the data, and present some preliminary results.
Paradoxical reference frequency shifts during paired flights in Japanese horseshoe bats evaluated with a Telemike.
Authors: Furusawa Yuto , Hiryu Shizuko , Riquimaroux Hiroshi
Published: March 2010

In order to examine vocal behaviors for the echolocating bats to improve extraction of jammed echolocation signals, group flight experiments were conducted where two Japanese horseshoe bats were flown simultaneously in a flight chamber. Horseshoe bats are known to conduct Doppler-shift compensation, keeping their echo CF2 frequency constant to which their auditory system is sharply tuned. It was hypothesized that bats shifted their reference frequencies apart to avoid overlapping the reference frequencies. Echolocation sounds during sequential flights were recorded with an onboard wireless microphone, Telemike. Reference frequencies were investigated by measuring Doppler-shift compensated CF2 frequencies of the bats’ own echoes. Recorded data show that the bats kept their echo CF2 frequency constant with a standard deviation (SD) of 50–80 Hz, indicating that they exhibited Doppler-shift compensation with the same accuracy as that used for flying alone (SD = 83.2 Hz). However, the bats did not shift their reference frequency toward increasing the frequency difference even when the initial difference in the reference frequencies between individuals was less than 100 Hz. Rather, the bats tended to make their reference frequencies closer during group flight compared to those for single flights. These findings suggest that multiple bats may squeeze their echo CF2 frequencies into a narrow frequency range. In addition, horseshoe bats may adapt to acoustic interference without expanding the frequency difference between individuals. [Work supported by ONR grant.]
Mode-2 internal waves impact on acoustic signal properties.
Authors: Orr Marshall
Published: March 2010

The properties of mode-2 internal waves repeatedly observed on the New Jersey Shelf (USA) with high-frequency acoustic flow visualization systems will be overviewed. The impact of the mode-2 internal waves on the range/depth distribution of acoustic signal properties will be discussed.
Periodicity of intensity fluctuations in shallow water in the presence of solitary internal waves.
Authors: Yang T. C.
Published: March 2010

This paper investigates the intensity variation with time of a broadband signal in the presence of moving solitary internal waves. The auto-correlation of the received impulse responses summed over a vertical line array of receivers (the so called Q function) is measured from the SWARM95 data using broadband pulses received on the NRL array at a range ∼42 km from the source. The signals are m-sequences centered at 400 Hz with a bandwidth of 100 Hz. The peak of the Q function shows a periodicity of 0.042 cycles/min, with a value changing with time depending on the position of the internal wave packets. Coupled mode equation is used to calculate mode coupling induced by the solitary internal waves and explain the observed periodicity of the intensity fluctuations. The results suggest that the positions and some parameters of the solitary waves could be remotely estimated from underwater sensors. [Work supported by the Office of Naval Research.]
Reverberation clutter from combined internal wave refraction and bottom backscatter.
Authors: Tang Dajun , Henyey Frank
Published: March 2010

A hypothesis is proposed that one mechanism for clutter observed in shallow water reverberation measurements is due to the combined effect of forward scatter and subsequent backscatter. The forward scatter refracts part of the sound from low grazing angle to high grazing angle, then being backscattered by bottom roughness. The refracted sound impinges onto the bottom at higher grazing angle, resulting in higher backscatter because of elevated bottom scattering cross section as compared to that at lower grazing angles. The resultant reverberation will stand out as a target-like clutter. An example is presented as a non-linear internal wave propagates in a shallow water channel, resembling conditions found on the New Jersey Shelf. The effect on reverberation of the internal wave as clutter is investigated using a time-domain numerical model. The model uses parabolic equation for the two-way propagation and first order perturbation approximation for bottom backscatter. [Work supported by ONR.]
Acoustic wave propagation and scattering in turbulence and internal waves.
Authors: Yamamoto N Tokuo
Published: March 2010

Acoustic wave propagation and scattering in turbulence and internal waves in Kanmon Strait and the outer New Jersey shelf are measured in a bistatic source-receiver configuration at frequency 5500 Hz. While internal wave dominates on the open New Jersey shelf, the turbulence dominates in the Kanmon Strait channel. Initially strong internal wave scattering is reduced rapidly due to strong mixing in the shallow strait. On the flat and open continental shelf, internal wave and warm water intrusion dominate while turbulence is near absent. The parabolic equation code predictions agree with data very well. The bistatic scattering data are processed for bistatic angles and the effects of Doppler shift on the mean flow and the broadening of peek spectra on the turbulent fluctuations. The mean flow and turbulence fluctuation obtained from the Doppler shift agreed with the two parameters obtained by the reciprocal acoustic transmission.
Dodecaperfluoropentane emulsion for oxygen delivery.
Authors: Unger Evan , Matsunaga Terry , Witte Russel , Olafsson Ragnar , Kerschen Arthur , Dolezal Melissa , Johnson Jenny
Published: March 2010

Dodecaperfluoropentane emulsion (DDFPe) was prepared from DDFP and surfactant PEG-Telomer-B and studied for particle sizing, storage stability, acoustically in vitro at 37 °C, and for oxygen transport in porcine model of hemorrhagic shock and as radiation sensitizer in murine model of tumor hypoxia. DDFPe had mean particle size of about 200 nm stable on storage at room temperature for over 2 years. Compared to microbubbles of perfluorobutane (PFB), more than 100-fold higher DDFPe was needed for comparable acoustic backscatter compared to PFB. Acoustic reflectivity increased with higher MI ultrasound but was still much less for DDFPe than for PFB. DDFPe was highly effective oxygen therapeutic in models of hemorrhagic shock and tumor hypoxia. A dose of as little as 0.6 cc/kg of DDFPe was sufficient to prevent death from hemorrhagic shock. In hypoxic tumors a similar dose reversed tumor hypoxia and restored sensitivity to radiation therapy. No ultrasound was used in these experiments for in vivo oxygen delivery. Compared to liquid perfluorocarbons which have been studied as oxygen therapeutics, DDFPe uses a much lower dose, about 1%. DDFPe is a promising oxygen transport therapeutic. Additional work is underway to try to develop DDFPe for this application.
Phase change nanodroplet for sensitizer for thermal and cavitational effects of ultrasound.
Authors: Kawabata Ken-ichi , Asami Rei , Yoshikawa Hideki , Azuma Takashi , Umemura Shin-ichiro
Published: March 2010

Although HIFU therapy is very low invasive method for tumor treatment, its time inefficiency and the absence of focus detecting mechanism of current systems limit the number of applicable cases. For an improved HIFU tumor treatment system, we propose to utilize a non-echogenic liquid nanodroplet which turns into highly echogenic microbubbles upon non-therapeutic ultrasound pulses. Such a nanodroplet would give echographic information on the focus of HIFU when exposed to the pulse and accelerate HIFU treatment by enhancing the ultrasonic energy deposition as microbubble. As such a nanoparticle system, we developed a phase change nanodroplet (PCND) which consists of superheated perfluorocarbon nanodroplet coated with PEGylated phospholipids. Significance of PCND to enhance ultrasonically induced therapeutic effects was investigated on mice, rats, and rabbits. At frequencies of 2 and 3 MHz, it was found that the presence of PCND (and generated microbubbbles) halved the intensity threshold for inducing thermal damage. At frequency around 1 MHz, it was found that the PCND halved the threshold for inducing damage in murine tumor, and the damage was induced both by thermal and cavitational effects of ultrasound. [This work was in part entrusted by the New Energy and Industrial Technology Development Organization, Japan.]
Ultrasound-mediated tumor chemotherapy with drug-loaded phase-shift nanoemulsions.
Authors: Rapoport Natalya , Nam Kweon-Ho , Christensen Douglas A. , Kennedy Anne M.
Published: March 2010

This paper describes droplet-to-bubble transition in block copolymer stabilized perfluoropentane nanoemulsions used for ultrasound-mediated tumor chemotherapy. Three physical factors that trigger droplet-to-bubble transition in liquid emulsions and gels have been evaluated, namely, heat, ultrasound, and injections through fine-gauge needles. Among those listed, ultrasound irradiation was found the most efficient factor. Tumor accumulation of nanodroplets after systemic injections to tumor bearing mice was confirmed by ultrasound imaging. Efficient ultrasound-triggered drug release from tumor-accumulated nanodroplets was confirmed by dramatic regression of ovarian, breast, and orthotopic pancreatic tumors treated by systemic injections of drug-loaded nanoemulsions combined with tumor-directed therapeutic ultrasound. No therapeutic effect from the nanodroplet/ultrasound combination was observed without the drug, indicating that therapeutic effect was caused by the ultrasound-enhanced chemotherapeutic action of the tumor-targeted drug, rather than the mechanical or thermal action of ultrasound itself. The mechanism of drug release in the process ultrasonically activated droplet-to-bubble conversion is discussed. [The work has been supported by the NIH R01 EB1033 grant to N.R.]
Passive mapping of cavitation activity for monitoring of drug delivery.
Authors: Arvanitis Costas D. , Gyongy Miklos , Bazan-Peregrino Miriam , Rifai Bassel , Seymour Leonard W. , Coussios Constantin C.
Published: March 2010

Acoustic cavitation has been recently shown to have tremendous potential as a mechanism for releasing and enabling improved uptake and biodistribution of therapeutic agents for the pharmacological treatment of cancer, cardiovascular, and neurodengenerative diseases. Passive cavitation mapping makes it possible to localize, characterize, and quantify cavitation activity by detecting the acoustic emissions produced by cavitating bubbles on an array of receivers, which are then back-propagated to form a cavitation-selective image with high spatio-temporal accuracy. In the present study, a 64-element diagnostic linear array was used to construct passive cavitation maps during pulsed HIFU exposure of a narrow channel transporting fluorescent dextran nanoparticles through a biocompatible porous hydrogel in the presence or absence of ultrasound contrast agents. Spectral analysis of the resulting acoustic emissions confirmed that different cavitation regimes were successfully instigated over the HIFU parameter range that was investigated. Superposition of cavitation selective images over the treatment course was used to construct maps of cavitation activity and dose as a function of location for treatment assessment and was found to correlate well with dextran extravasation. It is concluded that passive mapping of cavitation activity shows great promise for assessment and real-time monitoring of cavitation based drug delivery.
Dynamic response of bubbles within a compliant tube.
Authors: Jang Neo , Zakrzewski Aaron , Jensen Christopher , Halm Robert , Gracewski Sheryl M.
Published: March 2010

The dynamic response of bubbles in a liquid that are partially constrained by a surrounding tube or channel is important in a variety of fields, including diagnostic and therapeutic biomedical ultrasound and for microfluidic devices. In this study, numerical simulations, lumped parameter models, and experiments are used to investigate the effects of a surrounding tube on a bubble’s response to acoustic excitation. In particular, a coupled boundary element and finite element model and COMSOL MULTIPHYSICS models have been developed and used to investigate the nonlinear interactions of this three-phase system. Simulation results were compared to experimental measurements obtained using a scaled balloon model. The effects of tube parameters and bubble interactions on a bubble’s natural frequency important for proposed clinical applications of ultrasound are investigated. Resonance frequencies agree well with one-dimensional lumped parameter model predictions for a bubble well within a rigid tube, but deviate for a bubble near the tube end. Simulations also predict bubble translation along the tube axis and the aspherical oscillations and induced tube stresses at higher amplitudes. [Work supported by NIH and NSF CMMI.]
Effects of vaporized phase-shift nanoemulsion on high-intensity focused ultrasound-mediated heating and lesion formation in gel phantom.
Authors: Zhang Peng , Porter Tyrone
Published: March 2010

In this study, we demonstrate the feasibility of using a phase-shift nanoemulsion (PSNE) as nuclei for bubble-enhanced heating and lesion formation during high-intensity focused ultrasound (HIFU) thermal ablation. In our experiments, different concentrations of PSNE (5%–15%) uniformly distributed throughout gel phantoms made from acrylamide and albumin were sonicated with a 1.1 MHz HIFU transducer. The PNSE at the transducer focus were first vaporized into bubbles and then acoustically driven with continuous wave HIFU at different amplitudes. Bubble-enhanced heating resulted in albumin denaturation and lesion formation. HIFU-mediated heating was conducted with and without vaporized PSNE, and the lesion size and location relative to the transducer focus were measured after HIFU exposure. In the presence of vaporized PSNE, lesions were formed more rapidly and reached a larger volume compared with no vaporized PSNE. We also noted that lesions formed due to bubble-enhanced heating were more often prefocal due to backscattering from the bubble cloud. Our results show that these effects were more pronounced at higher PSNE concentrations. Finally, a comparison between the effects of pulsed and cw exposure on cavitation activity and lesion shape was investigated.
Optimal spherical array modal beamformer in the presence of array errors.
Authors: Sun Haohai , Yan Shefeng , Svensson U. Peter
Published: March 2010

Spherical array modal beamforming has become an attractive technique, since three-dimensional beampatten synthesis is more flexible than other array geometries, and the modal beamforming can be performed using the elegant spherical harmonics framework. However, the performance of a modal beamformer in practical situations is known to degrade in the presence of array errors caused by non-perfect spatial sampling, sensor sensitivity and phase variations, and sensor self-noise. Although the white noise gain constraint has been widely used to control the robustness of modal beamformers, it is not clear how to properly choose the constrained parameter set based on the known range of errors. In this paper, a worst-case performance optimization approach is formulated for the spherical array modal beamformer to improve its robustness against the above mentioned errors occurring in practice; thus the optimum performance can be obtained based on the known maximum level of errors. The robust optimal modal beamforming problem is reformulated as a convex optimization within the spherical harmonics framework, which can be efficiently solved by using second order cone programming.
Analysis of the high-frequency extension for spherical eigenbeamforming microphone arrays.
Authors: Meyer Jens , Elko Gary W.
Published: March 2010

The em32 Eigenmike® spherical microphone array is constructed with 32 omnidirectional pressure microphones mounted on the surface of a 8.4-cm rigid spherical baffle. Beamforming is accomplished by the spherical harmonic decomposition eigenbeamformer and modal-beamformer concept. Due to the array size, geometry, and average element spacing, this approach yields fully controllable beampattern control up to approximately 8 kHz. Above this frequency, spatial/modal aliasing begins to interfere with beampattern control. However, professional audio applications require an operating bandwidth to much higher frequencies. One solution is to use a single microphone capsule that is closest to the main axis of the beampattern direction at higher frequencies. It will be shown that there are some problems to this solution. As an alternative implementation it is shown that using a small subset of microphone capsules at high frequencies allows one to smoothly transition the beampattern from eigenbeamformer processing to higher frequencies.
Experimental study of synthetic aperture microphone array on rotor blade noise.
Authors: Lee Jaehyung , Rhee Wook , Choi Jong-Soo
Published: March 2010

Recent development of signal processing technologies has encouraged the aero-acousticians to implement the state-of-the-art sensors and data acquisition devices. They sometimes cost too much; however, especially for the academic arenas, the efforts of reducing the expense of integrating a system and increasing performance of phased array have initiated the idea of designing the synthetic aperture microphone array. The application of beamforming technique in localizing rotor blade noise and the use of synthetic aperture array in wind tunnel testing are presented. To apply the synthetic aperture beamforming on rotating objects, three steps should be considered. The first step is to restore the original acoustic waveform radiated from a rotating sound source. The second step is to synthesize independent array measurement data by correcting phase information of the received acoustic signals. Finally, the beamformer calculates the power on each point of grid in the space. The paper describes the details of deploying the synthetic aperture microphone array and the data reduction methods associated with acoustic measurement in wind tunnel. The comparisons of various patterns of synthetic aperture array are made. The beampower maps for rotor blade noise of various flight conditions are presented.
Non-uniform array synthesis concept and theory.
Authors: Huang Dehua
Published: March 2010

Uniform or symmetric array is a common practice for most of the sonar array design, where the same performance transducer elements are used for numerical simulation and manufacture engineering conveniences. However, non-uniform array designs show their advantages for special array applications. This paper will theoretically address the non-uniform array synthesis concept and theory. A few numerical examples will also be presented for element hybrid and cluster special arrays. [The work is supported by the U.S. Navy.
Effects of tempo and other musical features on stress responses to college students.
Authors: Wang Wei-Chun
Published: March 2010

It is believed that music has the power to soften emotions and alleviate pains. This study is aimed to explore the effects of tempo and other musical elements on stress-associated responses of college students when they listen to music. The effects of musical experience, preference, and awareness of music content on stress ratings are also investigated. College students were asked to listen to eight recorded musical excerpts and fill in a questionnaire to rate their relaxation and anxiety levels in a Likert five-point scale and to specify the musical elements. With a variety of tempo being considered, the musical excerpts were chosen from different types of music, including western classical music, Chinese pop music, Chinese traditional music, rock music, jazz blue, and new age music. Preliminary results showed that there was a correlation between relaxation and tempo, and the degree of personal music preference promoted stress reduction. It suggests that music used to enhance relaxation should match a person’s musical taste.
Characterization of the heat flux through the heat exchangers of a thermoacoustic cooler.
Authors: Poignand Gaëlle , Blanc-Benon Philippe , Jondeau Emmanuel , Gaviot Etienne , Camberlein Lionel , Penelet Guillaume , Lotton Pierrick
Published: March 2010

A small-scale standing wave thermoacoustic cooler with a couple of stack and heat exchangers is studied. In addition to classical instrumentation in such a device, thermal heat flux sensors specifically developed using MEMS technology equipped the heat exchangers of this refrigerator. These sensors give the temporal evolution of the heat fluxes through the hot and the cold heat exchangers. Hence, they provide a better understanding of heat transfer between the stack and the heat exchangers. In this work, the temporal evolution of the temperature along the stack and of the heat flux through the heat exchanger is measured versus the acoustic pressure. The results show that for high-pressure levels, the heat flux extracted at the cold exchanger rapidly increases until a maximum value and then stabilizes at a lower value. The origin of this limitation may come from the formation of vortices behind the stack highlighted in the work of Berson et al. [Heat Mass Transfer 44, 1015–1023 (2008)]. This work is supported by ANR (project MicroThermAc NT051_42101).
Determination of bubble size distributions in an ultrasonic cavitation field.
Authors: Labouret Stéphane , Frohly Jacques
Published: March 2010

An electromagnetic method is proposed for determining bubble size distribution in the range 2–12 m in ultrasonic cavitation fields. The method is used to investigate the effect of the continuous and pulsed irradiations and of the presence of increasing concentration of a surfactant (sodium dodecyl sulfate) on the bubble size distribution in a standing wave ultrasound field. The electromagnetic sizing technique shows considerable promise as a means of tracking changes in the bubble size distribution during insonation and determining the role of such changes in transitioning from a field that contains a few discrete bubbles to one that exhibits widespread cavitation activity.
Different regimes of nonlinear pulse propagation in porous medium.
Authors: Turo Diego , Umnova Olga
Published: March 2010

High-amplitude pulse propagation in rigid porous media has been investigated numerically and experimentally. At high-sound levels, strong interactions between different spectral components of the pulse make any frequency domain models difficult to use, therefore a time domain approach has been applied for the present research. The effect of Forchheimer nonlinearity (i.e., flow resistivity growth with particle velocity amplitude) in porous media is well studied. However, much less is known about the influence of memory effects on high-amplitude pulse propagation. The aim of this work is to study their relevance for high-amplitude pulses of different durations. A numerical finite difference time domain scheme has been developed which accounts for second order convection nonlinearity, Forchheimer correction, and memory effect simultaneously. It is shown that Forchheimer nonlinearity dominates for longer duration high-amplitude pulses, while convection terms and memory effect contribution become noticeable for shorter pulses of moderate amplitude. The numerical results are confirmed in a series of experiments with different duration pulses in the amplitude range from 120 Pa to 40 kPa.
Directivity and frequency control of an intense underwater laser acoustic source for navy applications.
Authors: Hornstein Melissa , Jones Theodore , Ting Antonio , Nicholas Michael
Published: March 2010

We develop an intense laser acoustic source, in which a tailored laser pulse can compress underwater at a predetermined remote location. Optical compression results in laser-induced breakdown (LIB), localized heating, and acoustic shock generation. Recent experiments include near-field acoustic source characterization using lens-focused 400-, 800-, 532-, and 1064-nm pulses of Ti:sapphire and Nd:YAG lasers. Sound pressure levels over 215-dB were achieved using a compact laser. We have demonstrated control of the shape of the LIB plasma volume, and thereby control of the acoustic frequency spectrum and acoustic source directivity. By superposition of volume elements within the LIB, the acoustic pulse duration in a given propagation direction is determined by the parallel dimension of the LIB, divided by the parallel acoustic transit time across the LIB. Thus, the shape of the LIB strongly affects the acoustic pulse duration and directivity, and aspherical LIB volumes result in strongly anisotropic acoustic sources. In our experiments, the LIB volume shape was varied by laser pulse length, energy, optical bandwidth, and focusing angle. We also studied acoustic propagation in a 30 000-gal bubbly salt water tank. [This work is supported by the U.S. Office of Naval Research.]
Exploring the traveling wave dispersion in the cochlea.
Authors: Ramamoorthy Sripriya , Zha Ding-Jun , Nuttall Alfred L
Published: March 2010

In the measurements of the basilar membrane velocity as well as the auditory nerve responses to acoustic stimulation, it has been observed that low frequencies arrive at the measurement location (or the tonotopically located auditory nerve fiber) earlier and high frequencies arrive later, with significant delay noticed in the characteristic frequency component. In the derived impulse responses as well as click responses, this phenomenon manifests as the instantaneous frequency glide from low to high frequencies. The origin of these frequency glides has not yet been satisfactorily explained. In this paper, a simple elucidation along with experimental validation using measurements made on guinea pigs is presented for the plausible origin of the frequency glides observed in the cochlea.
Otoacoustic emission suppression tuning curves in humans.
Authors: Gorga Michael, P. , Neely Stephen, T. , Kopun Judy, G. , Tan Hongyang
Published: March 2010

DPOAE suppression data as a function of suppressor level (L3) for f2 frequencies from 0.5 to 8 kHz and L2 levels from 10 to 60 dB SL were used to construct suppression tuning curves (STCs). DPOAE levels in the presence of suppressors were converted into decrement versus suppressor level (L3) functions, and the L3 resulting in 3-dB decrements was obtained by transformed linear regression. These L3 levels were plotted as a function of f3 to construct STCs. STCs when f3 is plotted on an octave scale were similar in shape across f2 frequency. These STCs were analyzed to provide estimates of gain (tip-to-tail differences) and tuning (QERB). Both gain and QERB decreased as L2 increased, regardless of f2, but the increase with f2 was not monotonic. A roughly linear relation was observed between gain and QERB at each frequency, such that gain increased by 4–13 dB (mean xa1;xd6; 8 dB) for every unit increase in QERB, although the pattern varied with frequency. These findings suggest consistent nonlinear processing across a wide frequency range in humans, although the nonlinear operation range is frequency dependent. [Work supported by the NIDCD R01 2251 and P30 4662].
The influence of practice on the discrimination of spectro-temporal modulation depth.
Authors: Sabin Andrew T. , Eddins David A. , Wright Beverly A.
Published: March 2010

The pattern of sound energy spread across frequency and time (spectro-temporal modulation) is a crucial stimulus cue for sound identification. Improvements in the sensitivity to this modulation could potentially aid performance on numerous real-world tasks, yet it is unknown how practice influences this sensitivity. To investigate this issue, normal-hearing adults (n=8) were trained ∼1 h/day for 7 days to discriminate between noises with the same spectro-temporal modulation drifting upward in audio frequency but with different modulation depths. Performance on the trained condition and on four untrained conditions was examined both before and after the training phase. Depth-discrimination thresholds improved significantly on the trained condition and on an untrained condition with a downward-drifting modulation. Discrimination thresholds also improved in subsets of listeners on untrained isolated component modulations (spectral or temporal) of the trained spectro-temporal modulation. Finally, the ability to detect the trained spectro-temporal modulation worsened significantly in proportion to the amount of improvement on the trained discrimination task. These data suggest that training on depth discrimination may be a means of improving sensitivity to spectro-temporal modulation depth in real-world stimuli, but potentially at the cost of the ability to detect these modulations. [Work supported by NIH/NIDCD]
Relationship between physiological and psychoacoustical sensitivity to amplitude and frequency modulation.
Authors: Hsieh Michelle , Champlin Craig , Jin Su-Hyun
Published: March 2010

Various researchers have found a correlation between the auditory steady state response (ASSR) and corresponding behavioral measurements such as speech recognition scores [e.g., Dimitrijevic et al. (2001)]. However, relatively few studies have examined the sensitivity to small changes in amplitude and frequency modulation depths. In the present study, it was hypothesized that physiological individual differences in sensitivity to amplitude and frequency modulation depths would be reflected in corresponding psychophysical measures. Auditory steady-state responses were collected in response to amplitude- and frequency-modulated pure tone carriers (500 and 3000 Hz) in normally hearing listeners over a range of modulation depths at several different modulation rates. Participants also completed a psychophysical task in which they were asked to detect the modulated tone in a two-interval forced choice testing paradigm. The relationships between the ASSR and the psychophysical performance will be discussed.
A hybrid procedure for psychometric function estimation.
Authors: Patra Harisadhan , Valente Daniel L. , Jesteadt Walt
Published: March 2010

Threshold, defined as the stimulus level required for a predefined percent correct response, is often used to measure a listener’s performance. Psychometric functions (PFs) provide better insight to the underlying decision process. Two parameters, threshold (α) and slope (β), are sufficient to define a PF. Estimation of α and β from individual trials of adaptive procedure tracks is time-consuming, costly, and dependent upon the step-size choice. A procedure has been developed and written in MATLAB, which provides stable PF parameter estimates of α and β and also their confidence intervals. The procedure consists of three stages. First, signals are presented adaptively to estimate levels corresponding to 71% and 87% correct. Second, the signal is pseudo-randomly presented at one of five fixed levels equally spaced over that range. Finally, the program implements a maximum-likelihood procedure updated after every trial to estimate signal levels corresponding to 63%, 71%, 76%, 79%, and 87% correct. After 140 trials, the program estimates α and β from the entire run and generates a PF curve that typically accounts for at least 90% of the total variance. The reliability and validity of the procedure are analyzed using simulations and observed data. [Work supported by NIH.]
The effect of stimulus context on cortical measures of pitch processing using functional magnetic resonance imaging.
Authors: García Daphne , Plack Christopher , Hall Deborah
Published: March 2010

Many different paradigms and pitch-evoking stimuli have been used to study pitch. A growing body of neurophysiological evidence shows that cortical responses are sensitive to the context from which stimuli are presented. In this human fMRI study, we tested the hypothesis that the stimulus context influences the pattern of pitch-related auditory cortical activation. Fifteen listeners participated in a blocked design experiment. A diotic harmonic complex tone and a dichotic Huggins pitch stimulus were presented within either a noise or silent context and activation was contrasted with matched noise control conditions. Results revealed significant main effects of both context (noise/silence) and pitch stimulus (diotic/dichotic) (p < 0.05, corrected). While the response to context was primarily localized in primary auditory cortex, the response to pitch was more posterior. The context significantly modulated the pitch response, especially in subregions of planum temporal; non-primary auditory cortex. While the response to the diotic pitch was greater than the dichotic pitch, the overall results were broadly comparable. We therefore conclude that if the feature specificity of the pitch-related response is to be inferred from fMRI data, future studies should include careful controls for stimulus context.
Target enhancement and noise cancellation in the identification of rudimentary sound sources in noise.
Authors: Lutfi Robert A. , Liu Ching-Ju , Stoelinga Christophe N.J.
Published: March 2010

The identification of targets in noise is believed to entail two processes, one that acts to enhance the target and the other to cancel the noise [Durlach et al. (2003). J. Acoust. Soc. Am. 2984–2987]. The relative contribution of these processes in the identification of rudimentary sound sources is unknown. In the present study, perturbation analysis was used to determine the relative contribution in terms of the sign and magnitude of listener decision weights on the noise. In a two-interval, forced-choice procedure, listeners identified as target the impact sound produced by the larger of two stretched membranes. The noise on each presentation was the impact sound of a variable-sized plate. For four of five listeners showing significant interference, the weights were positive indicating enhancement; for the remaining listeners, they were negative indicating cancellation. In a second condition, the target was the membrane hit with harder force, and the noise was a plate hit with variable force. The noise weights for all listeners in this condition indicated cancellation. The results are consistent with an interpretation in which noise cancellation is the predominant strategy for identifying targets unless it is precluded by uncertainty regarding the spectral properties of the noise. [Research supported by NIDCD Grant No. 5R01DC006875-05].
The effect of binaural coherence on envelope interaural time difference thresholds.
Authors: Monaghan Jessica J. M. , Krumbholz Katrin , Seeber Bernhard U.
Published: March 2010

Room reflections alter the envelope of sounds differently at both ears, reducing binaural coherence. Experiment 1 measured interaural time difference (ITD) discrimination thresholds for broadband and transposed speech. A sentence was convolved with binaural room impulse responses for different source-receiver distances, and the envelopes extracted and multiplied with 4-kHz tones. Preliminary results indicate that envelope ITD thresholds increased from <100 μs without reverberation to >700 μs at four times the reverberation radius. ITD thresholds for unprocessed speech were more robust to the addition of reverberation, only rising above 350 μs at the same distance. To investigate whether reverberation is detrimental owing to reduction in binaural coherence, stimulus envelopes were created by temporally jittering raised cosine pulses around a 10-ms separation. Bilaterally independent jittering allowed variation in coherence while minimizing change in other envelope parameters. Preliminary results show ITD thresholds <100 μs for coherent envelopes, increasing to >700 μs for coherences of 0.6, a value consistent with the room simulations above. Envelope coherence strongly affects ITD discrimination, suggesting that ITDs extracted from high-frequency channels may not provide useful information in many realistic situations. This has implications for bilateral cochlear implant users, as current devices provide ITDs only in envelopes.
The use of confusion patterns to evaluate the neural basis for concurrent vowel identification.
Authors: Chintanpalli Ananthakrishna , Heinz Michael G.
Published: March 2010

Perceptual studies of concurrent vowel identification suggest that listeners with normal hearing (NH) are better able to use differences in fundamental frequency (F0) than listeners with sensorineural hearing loss (SNHL). However, the neural basis for this difference remains unknown. The present study sought to validate a neural model of concurrent vowel identification based on specific confusion patterns made by NH listeners. A standard set of five vowels was used. In each concurrent vowel pair, vowel 1 had F0 = 100 Hz, while the F0 of vowel 2 was varied between 100–126 Hz (4 semitones). NH listeners made similar confusions across all F0 differences, with a reduction in occurrence as F0 difference increased. F0 benefit varied significantly across concurrent vowel pairs. A phenomenological auditory-nerve model was cascaded with F0 segregation algorithms to predict the perceptual observations. Neural predictions showed similar confusion patterns to the perceptual data for many (but not all) concurrent vowel pairs. Validating a NH physiological model with specific confusion patterns will allow the model to be used to predict effects of specific physiological changes related to SNHL, which may be useful for improving cochlear-implant and hearing-aid signal processing strategies. [Work supported by Purdue University.]
Noise robust representation of speech in the primary auditory cortex.
Authors: Mesgarani Nima , David Stephen , Fritz Jonathan , Shamma Shihab
Published: March 2010

It is well known that humans can robustly perceive phonemes despite substantial variability across speakers, context and natural distortions. This study examines the responses of neurons in primary auditory cortex (A1) to phonetically labeled speech stimuli in clean, additive noise and reverberant conditions. Using a linear decoder [Bialek (1991)] to reconstruct the input stimulus spectrogram from the population response, we observed that spectrograms reconstructed from the neural responses to noisy speech were closer to the original clean spectrograms than to the noisy ones. This indicates that sound representations in A1 serve to enhance information about natural speech signals relative to noise, thus extracting signal from noise. Examining the average reconstructed phoneme spectrograms in clean and noisy speech revealed a remarkable robustness in the encoding of features important for discrimination of different phonemes. In addition, it was found that the strict linear spectro-temporal receptive field (STRF) model of A1 neurons is insufficient to explain the noise robustness observed in the neural data. However, when a non-linear synaptic depression is integrated into the inputs for the STRF model, the noise was reduced in the reconstructed spectrograms similar to what observed with the actual neural data.