bluuebunny/crossref_metadata_2025 huggingface dataset:
Otoacoustic emission sensitivity to exposure to styrene and noise
Authors: Sisto R. , Cerini L. , Gatto M. P. , Gherardi M. , Gordiani A. , Sanjust F. , Paci E. , Tranfo G. , Moleti A.
Published: November 2013

The ototoxic effect of the exposure to styrene is evaluated, also in the presence of simultaneous exposure to noise, using otoacoustic emissions as biomarkers of mild cochlear damage. Transient-evoked and distortion product otoacoustic emissions were recorded and analyzed in a sample of workers (15 subjects) exposed to styrene and noise in a fiberglass manufacturing facility and in a control group of 13 non-exposed subjects. Individual exposure monitoring of the airborne styrene concentrations was performed, as well as biological monitoring, based on the urinary concentration of two styrene metabolites, the Mandelic and Phenylglyoxylic acids. Noise exposure was evaluated using wearable phonometers, and hearing loss with pure tone audiometry. Due to their different job tasks, one group of workers was exposed to high noise and low styrene levels, another group to higher styrene levels, close to the limit of 20 ppm, and to low noise levels. A significant negative correlation was found between the otoacoustic emission levels and the concentration of the styrene urinary metabolites. Otoacoustic emissions, and particularly distortion products, were able to discriminate the exposed workers from the controls, providing also a rough estimate of the slope of the dose-response relation between otoacoustic levels and styrene exposure.
Toward reliable metrics for Sacred Harp singing spaces
Authors: Copenhaver Benjamin J. , Schoen Scott J. , Haberman Michael R.
Published: November 2013

Sacred Harp singing, a common type of shape-note singing, is a centuries-old tradition of American community choral music. It is traditionally a participatory form of music with no distinction between performers and audience, a characteristic that makes for acoustical requirements that differ considerably from those of a concert hall or even a typical worship space. In the spirit of the text Concert Halls and Opera Houses by L. Beranek, we seek to correlate acoustical measurements of spaces used for Sacred Harp singing with subjective evaluations of those spaces made by the singers themselves. To achieve this, measurements of reverberation time and support factor of each space are coupled with participant surveys in 10 different Sacred Harp singing locations. Those measurements are then examined for their applicability as metrics for evaluation of Sacred Harp performance spaces. In addition, various measurement techniques for this type of space are explored and reported.
Human responses to impulsive noises with accompanying rattle
Authors: Hathaway Andrew , Hanna Kristin , Wang Lily M.
Published: November 2013

This research aims to quantify human reactions to short impulsive noise bursts with a rattle element, to complement research at NASA Langley Research Center on evaluating human response inside buildings to low-level sonic booms. While previous research has demonstrated effects of noise bursts of varying amplitudes on assorted cognitive tasks, more information is needed to indicate at what level and to what degree such noise bursts may impact human performance and perception. It is also thought that the addition of rattle, produced from the noise burst exciting assorted elements inside the building, could prove more detrimental to human responses than noise bursts alone. Seventeen participants each completed twelve 30-min sessions during which they were subjected to controlled yet randomly occurring 250 ms broadband noise bursts, either with or without a rattle component, while completing an arithmetic task utilizing working memory. Four different levels of noise bursts, from 55 to 70 dBA, were tested; accompanying rattle components were set to be 4 dBA louder than the associated burst, generated by a separate audio source. Results will be presented and compared to those from a similar test using just broadband noise bursts alone. [Work supported by a NASA Nebraska Space Grant.]
The do’s and don’ts of electronic sound masking
Authors: Wowk Roman
Published: November 2013

Electronic sound masking, when properly implemented, can be an effective tool for introducing background noise in occupied spaces, which is a key factor of speech privacy. Mechanical ventilation systems generally cannot be relied upon to provide the consistent and appropriate levels of background noise that sound masking systems are capable of, and this is even more the case with variable-air-volume systems and several emerging (or re-emerging) technologies such as natural ventilation, underfloor air distribution, and chilled beams. However, despite general industry consensus of what constitutes appropriate levels of background noise, striking discrepancies in acoustic performance have been observed for several recent sound masking installations, thus defeating the original objectives for such a system. Fortunately, such issues can be avoided if design efforts account for limitations of both the sound masking system and acoustics of the space, clear performance requirements are established, and the system is properly adjusted and balanced prior to occupancy. Through case studies, this paper seeks through to illustrate the need for a guided approach toward achieving successful outcomes while also highlighting the broader range of issues involved with speech privacy.
Long term passive acoustics monitoring reveals differences in deep diving Odontocetes foraging strategies
Authors: Giorli Giacomo , Au Whitlow W.
Published: November 2013

Beaked whales, sperm whales, pilot whales, and Risso's dolphins perform deep dives to feed on prey in the deep sea. They use echolocation to detect prey, and echolocation can be monitor as a proxy of their foraging activities. Ecological acoustic recorders were deployed to monitor in time the echolocation signals of pilot whales, Risso's dolphins, beaked whales, and sperm whales near Josephine Seamount (Portugal), in the Ligurian Sea (Italy), and along the Kona coast of the island of Hawaii. Data analysis was performed using two automatic detector/classification systems: Marine Mammal Monitoring on Navy Ranges (M3R), developed at the Naval Undersea Warfare Center Division in Newport, USA, and a custom MATLAB program. An operator-supervised custom MATLAB program was used to validate the classification performance, which was higher than 85% for each category. Results show that pilot whales and Risso's dolphins concentrate their feeding effort mainly during the night. The foraging activity of beaked and sperm whales is variable, and different patterns are observed at different locations. Prey behavior might play a central role in driving the foraging activity of deep divers, but to date, the reasons why such activity varies between species that might feed on similar food resources remains unknown.
A modified wavefront curvature method for the passive ranging of echolocating dolphins in the wild
Authors: Ferguson Eric L.
Published: November 2013

Passive ranging by wavefront curvature is a practical nonintrusive method for studying the behavior of echolocating odontocetes (toothed whales including dolphins) in their natural habitats. This method requires two differential time-of-arrival measurements of the signal wavefront using three hydrophones, which are widely spaced along a straight line. However, if the middle hydrophone is displaced (even by a small amount) from an imaginary line connecting the other two (outer) sensors, then the source range estimate can be significantly biased. A modification to the method is shown to solve this problem so that the range bias is zero. The source locations of echolocating dolphins are estimated using the modified wavefront curvature method and they are found to match those estimated by other (line of position and circle intersection) methods. The application of the modified method to a series of dolphin click sequences demonstrates that the method is a powerful tool for studying the behavior of free-ranging echolocating dolphins in the wild. For example, individual dolphins are located with unprecedented accuracy even when multiple echolocating dolphins are present.
Hydrophone data management at Ocean Networks Canada
Authors: Pirenne Benoı̂t , Dorocicz John , Dakin Tom
Published: November 2013

In this contribution, we describe the seabed cabled observatory networks managed by Ocean Networks Canada (ONC). The focus is on the hydrophone hosting capabilities of ONC's advanced science infrastructure and on the assets already in place, together with their scientific objectives. We describe the data acquisition and archival principles and methods, as well as the derived products available to users. We also elaborate on the concerns of the United States and Canadian Navies with quasi real-time, public data and on the mitigation measures in place to balance security needs with the scientific and public safety goals of the instrumentation. Finally, we describe the potential for instrument development and testing that ONC offers on its networks.
Twinkling artifact of Doppler imaging for cavitation detection during high-intensity focused ultrasound therapy: Sensitivity and resolution
Authors: Li Tong , Khokhlova Tatiana D. , Sapozhnikov Oleg A. , Sapozhnikov Oleg A. , Hwang Joo Ha
Published: November 2013

The mechanism of the twinkling artifact (TA) during Doppler imaging of kidney stones is well-known and is hypothesized to stem from the irregular scattering of Doppler ensemble pulses from fluctuating microbubbles trapped in crevices of the kidney stone. We have previously demonstrated that the TA can be used to detect and image microbubbles in soft tissue during pulsed HIFU treatment. In this work, the characteristics of the method—the sensitivity to small bubbles and the spatial resolution—were investigated experimentally and compared to other passive and active cavitation imaging methods such as pulse inversion. An approach was proposed for quantification of the cavitation images provided by the method, and the resulting metric was compared to the inertial cavitation dose. The experiments were performed using pulsed 1-MHz HIFU exposures of transparent gel phantoms, ex vivo tissue and in vivo mouse model of pancreatic cancer. [Work supported by RFBR and NIH (EB007643, 1K01EB015745, and R01CA154451).]
Dual-frequency intravascular ultrasound transducer design for contrast agent imaging
Authors: Martin K. Heath , Ma Jianguo , Jiang Xiaoning , Dayton Paul A.
Published: November 2013

Intravascular ultrasound (IVUS) is a unique diagnostic tool for assessing the composition and degree of stenosis of atheromata in cardiovascular disease. As of yet, contrast enhanced IVUS has not been clinically implemented despite its potential to provide functional information, such as degree of plaque vascularization, in conjunction with standard anatomical mapping. In this study, we demonstrate that nonlinear microbubble signals can be detected with minimal signal processing using an ultra-broadband IVUS transducer composed of a low frequency transmit and a high frequency receive combined element. Raw signals were acquired from a single element transducer (1 × 3 mm, fc = 6.5/35 MHz) after aligning to an acoustically transparent 200 µm inner diameter cellulose tube. Poly-disperse, (1–10 µm diameter) lipid-coated microbubbles were injected at high concentration (4.8 × 108 MBs/mL) and peak negative pressures were varied from −0.3 to −1.8 MPa while transmission cycles were increased from 1to 5. In vitro results indicate signal to noise ratios of 11 dB are attainable at 2nd harmonics and similar SNRs (10–8 dB) at higher harmonics. The results of this study indicate that contrast enhanced IVUS imaging is possible using a single transmit pulsing scheme enabled by using a dual- frequency broadband transducer design.
The late onset of nonlinear emissions from an ultrasound contrast agent
Authors: Shekhar Himanshu , Rychak Joshua J. , Doyley Marvin M.
Published: November 2013

Microbubble contrast agents (MCA) are currently being investigated for several diagnostic and therapeutic applications. The nonlinear emissions of MCA are important for imaging and therapy; therefore, they need to be thoroughly characterized. In this study, we to investigated the temporal changes in the nonlinear emissions from a phospholipid-coated MCA. We characterized the nonlinear emissions over 60 min at 10 MHz, with 64 cycle excitation pulses, 30—290 kPa pressures, and 1 kHz pulse repetition frequency. The second harmonic, subharmonic, and ultraharmonic response were measured relative to the fundamental signal from the agent backscatter spectra. It was observed that emissions at the second harmonic did not change appreciably over the measurement period. However, the emissions at the subharmonic and ultraharmonic frequency increased by 18 and 8 dB over 20 min (relative to measurements at t = 0) and then decreased slightly. The highest relative increase was observed within the first 5 min —a timescale that can be relevant for clinical applications. These findings could help avoid errors in quantitative estimates obtained from nonlinear imaging, pressure estimation, and therapy monitoring techniques. Further, an elaborate understanding this phenomenon could help design efficacious MCA for clinical applications.
Toward on-the-fly ray identification for RAFOS-2 navigation
Authors: Howe Bruce , Nosal Eva-Marie , Van Uffelen Lora J.
Published: November 2013

RAFOS-2 has been proposed as an undersea equivalent of GPS. By using broadband source signals and resolving the multipath arrival structure, long range positioning accuracy can be ~100 m as demonstrated by Van Uffelen et al., J. Acoust. Soc. Am. 133, 3444 (2013). Further improvement requires ray identification to be performed for each instantaneous position. Using the PhilSea10 experiment as a test case, we show that the range independent arrival pattern amplitude(range, depth, travel time; ray ID) can be simply parameterized. This may lead to more efficient algorithms for real time in situ navigation of mobile platforms. [Work funded by the Office of Naval Research.]
Acoustic localization of seagliders in the Philippine Sea using broadband transmissions from moored acoustic sources
Authors: Van Uffelen Lora J. , Howe Bruce , Nosal Eva-Marie , Carter Glenn , Worcester Peter , Dzieciuch Matthew
Published: November 2013

Seagliders obtain precise GPS positioning at surfacing events between dives, but can be underwater for several hours and travel several kilometers during a single dive, during which time less is known about the position of the glider. Four Seagliders deployed in the Philippine Sea from November 2010 to April 2011 were equipped with Acoustic Recorder Systems, enabling them to record over 2000 transmissions from five moored broadband acoustic sources at ranges up to 700 km and depths up to 1000 m. These sources sequentially transmitted linear FM sweeps from approximately 200 to 300 Hz at 9-min intervals. Source-receiver ranges, determined from travel-time offsets of the received pattern of acoustic arrival peaks, are combined for sets of source transmissions using the stochastic inverse method of least squares to estimate the position of the glider at the time of acoustic reception. Because the source transmissions are separated in time and because the glider is in constant motion, it can move appreciably between source receptions. A linear model of glider motion is incorporated into the least-squares analysis to account for this motion and to simultaneously estimate glider velocity. These acoustically derived estimates of glider position are compared with the positions estimated by a glider kinematic model.
Stages with high ceilings, pipe organs, and active acoustics
Authors: Schwenke Roger W. , Ellison Steve
Published: November 2013

Two case studies are presented of rooms that have a high ceiling over the stage to accommodate a pipe organ. Svetlanov hall is the principal venue of Moscow's International Performing Arts Center. It has two to four rows of chorus seating on two levels at stage left and right. The upstage wall is occupied by the largest pipe organ in Russia. It has a physical reverberation time of 1.7 s, which is within the accepted range for symphonic music, but longer reverberation times would be preferred for some pipe organ repertoire. Christopher Cohan Performing Arts Center at California Polytechnic State University has a proscenium and thrust stage. The Forbes Pipe Organ is housed on the stage right wall of the thrust stage. The symphony usually performs on the thrust stage entirely in front of the proscenium with the solid decorative fire curtain down. Both rooms had poor communication on stage between performers, which led them to implement a solution using active acoustics. In both rooms all of the active acoustic elements overhead of the stage are on motors and can be retracted when not in use.
Fin whales (Balaenoptera physalus) in British Columbia sing a consistent song
Authors: Koot Barbara , Ford John K. , Hannay David , Trites Andrew W.
Published: November 2013

Geographic differences in fin whale song that may be related to population structure have been documented in the Atlantic and Southern Oceans. However, information on the songs and population structure of fin whales in the North Pacific is limited. We analyzed fin whale songs recorded over 9 months by an Autonomous Underwater Recorder for Acoustic Listening device (AURAL, Multi-Electronique Inc.) deployed west of Vancouver Island, British Columbia (July 2010 to March 2011). Our analysis focused on internote intervals—the song characteristic that others have shown to display the most geographic variation. We found that beginning in mid-August and continuing to the end of our study, fin whales produced one stereotyped song consisting of alternating classic (C) and backbeat (B) notes. Internote interval evolved slightly over this time period, and small differences in interval length occurred among individual songs. However, all songs shared the same note arrangement (i.e., the interval between C and B notes was always 30% longer than the interval between B and C notes). All whales recorded in this study produced a similar song, suggesting that they may belong to the same acoustic population. Future studies will help to determine the spatio-temporal boundaries of this acoustic population.
Observations of region-specific fish behavior using long- and short-range broadband (1.5—6 + kHz) active acoustic systems
Authors: Stanton Timothy K. , Jech J. Michael , Gauss Roger C. , Jones Benjamin A. , Sellers Cynthia J. , Fialkowski Joseph M.
Published: November 2013

Two broadband active acoustic systems, in concert with traditional narrowband systems and nets, were used to study distributions of fish in three regions within the Gulf of Maine. The long-range multi-beam broadband system detected fish out to 15 km range and the downward-looking short-range broadband system detected fish throughout the water column close behind the ship. The multi-year (2007–2011) study revealed distinct spatial patterns of fish and corresponding echo statistics in each region—diffusely distributed, sparsely distributed compact patches, and long (continuous) shoals. The broadband capabilities of the sonar systems (each spanning 1.5—6 + kHz) uniquely allow observations of resonance phenomena of the local swimbladder-bearing fish. The observed resonances were consistent with the fish species, sizes, and depths that were concurrently sampled in each area from a second research vessel. Spectral peak analysis also interestingly revealed the presence of distinct modes, which may be useful indicators of mixed-species and/or mixed-sized (e.g., juvenile and adult) assemblages of fish. [Work supported by Office of Naval Research.]
Measurements of diel variation of acoustic backscatter power from phytoplankton
Authors: Kim Hansoo , Bok Tae-Hoon , Kim Juho , Paeng Dong-Guk , Shah Md Mahfuzur Rahman , Lee Joon-Baek
Published: November 2013

Phytoplankton is a primary producer in the ocean, and its vegetative activity plays an important role in controlling the global environment. In this study, the high-frequency acoustic signals were collected to evaluate the photosynthetic activity of phytoplankton during a day. The integrated backscatter power (IBP) from a dinoflagellate Cochlodinium polykrikoides was measured by a 5 MHz acoustic system during a 5-day cultivation period with a 14 h:10 h light:dark cycle. IBP increased by 0.6 dB in five days, but varied by 0.83 ± 0.1 dB during an irradiance cycle. The daily increase in IBP was a result of an increase in the number of cells during cultivation, while the diel variation was partly resulted from the variation of volume of cells by photosynthesis. In addition, cell division and separation might affect IBP. IBP of another dinoflagellate Amphidinium carterae Hulburt was also measured by a 10MHz transducer during a 3-day cultivation period while cell volume and photosynthetic capacity were measured four times a day (07:00, 12:00, 19:00, 24:00). This study suggests that high-frequency acoustics may be a meaningful tool to investigate the photosynthetic metabolism of a phytoplankton cell. [This work was supported by Defense Acquisition Program Administration and Agency for Defense Development under the contract UD130007DD.]
Acoustic mapping of ocean currents using networked distributed sensors
Authors: Huang Chen-Fen , Yang TsihC , Liu Jin-Yuan
Published: November 2013

Distributed underwater sensors are expected to provide oceanographic monitoring over large areas. As fabrication technology advances, low cost sensors will be available for many uses. The sensors communicate to each other and are networked using acoustic communications. This paper first studies the performance of such systems for current measurements using tomographic inversion approaches to compare with that of a conventional system which distributes the sensors on the periphery of the area of interest. It then proposes two simple signal processing methods for ocean current mapping (using distributed networked sensors) aimed at realtime in-buoy processing, Tomographic inversion generally requires solving a challenging high dimensional inverse problem, involving substantial computations. Given distributed sensors, currents can be constructed locally based on data from neighboring sensors. It is shown using simulated data that results obtained using distributed processing are similar to those obtained from conventional tomographic approaches. The advantage for distributed systems is that by increasing the number of nodes, one gains a much more improved performance. Furthermore, distributed systems use much less energy than conventional tomographic system for the same area coverage. Experimental data from an acoustic communication and networking experiment are used to demonstrate the feasibility of acoustic current mapping.
Low frequency scattering from fish schools: A comparison of two models
Authors: Raveau Maria P. , Feuillade Christopher
Published: November 2013

A theoretical comparison between two scattering models for fish schools was performed. The effective medium approach, based on the work of Foldy [Phys. Rev. 67, 107–109 (1945)], which has previously been used to describe scattering from bubble clouds, was used to calculate the variations of the scattering length of a fish school with frequency, and with azimuth. Calculations were also performed with a model used previously to study collective back scattering from schools of swim bladder fish, which incorporates both multiple scattering effects between fish, and coherent interactions of their individual scattered fields [J. Acoust. Soc. Am., 99(1), 196–208 (1996)]. Two different packing algorithms were used, in order to investigate the influence of the spatial distribution of fish on the scattering response of the school. Comparison of the two models shows good agreement in the forward scattering direction, where no frequency dependent interference effects are observed. The models indicate divergent results in the back scattering direction, where the arrangement of fish in the school strongly affects the scattering amplitude. The upper frequency limit of the effective medium approach is also discussed, and the effect of the depth of the school in the water column. [Research supported by ONR.]
Nonlinear dynamics and control of ultrasound contrast agent microbubbles
Authors: Carroll James M. , Lauderbaugh Leal K. , Calvisi Michael L.
Published: November 2013

The nonlinear response of ultrasound contrast agent microbubbles is well-known and is important for both diagnostic and therapeutic purposes. A model of thin-shelled, spherical contrast agents subject to ultrasound is presented based on a modified form of the Rayleigh-Plesset equation combined with terms to account for the shell influence. Techniques from dynamical systems theory are employed to analyze the model and elucidate the complex behavior of contrast agents forced by ultrasound. It is shown that the contrast agent can undergo a sequence of bifurcations as the acoustic pressure amplitude is increased, leading to a transition from periodic to chaotic oscillations at sufficiently large forcing. Yet even at high forcing, regions of periodic behavior exist. The response of the contrast agent, however, is strongly dependent on the shell properties and the applied acoustic forcing. Furthermore, a nonlinear, sliding mode controller is developed and applied to the spherical contrast agent model to demonstrate the feasibility of using the nonlinear controller to modulate the contrast agent response through the incident ultrasound. Applications of the nonlinear control system to contrast agents include radius stabilization in the presence of an acoustic wave, excitation of radial growth and subsequent collapse, and generation of periodic radial oscillations while a contrast agent is within an acoustic forcing regime known to cause a chaotic response.
Delay differential equations for single-bubble dynamics in a compressible liquid
Authors: Thomas Derek C. , Ilinskii Yurii A. , Hamilton Mark F.
Published: November 2013

Most common methods to include the effects of liquid compressibility in models for single-bubble dynamics rely on series expansions to some order in the inverse of the sound speed in the liquid. It has been shown that the Keller-Miksis model for single-bubble dynamics can be obtained from a series expansion of a delay differential equation related to the Rayleigh-Plesset equation for a single bubble. The iterative approach used to obtain the series expansion of the delay-based model becomes unworkable for more complicated models of bubble dynamics. Therefore, to provide an alternative, simpler method to model the effects of liquid compressibility, the delay differential equation model proposed by Ilinskii and Zabolotskaya [J. Acoust. Soc. Am. 92, 2837 (1992)] is analyzed directly. The results of the delay-based formulations are compared to those produced by models based on common series expansions. Alternative formulations of the delay differential equation are also considered and compared.
Spectral character of the resonator guitar
Authors: Ludwigsen Daniel
Published: November 2013

The resonator guitar was invented in the 1920s, with one or more metal cone resonators set into the body. These additions were originally meant to amplify the sound of the acoustic guitar for performance in a band. The distinct timbre of the resonator ensured that the design survived even after electrification, especially in blues and bluegrass genres. A study of the sound radiated from different models of resonator guitars, as well as a similar standard acoustic guitar, compares spectral features to understand the unique sound of the resonator guitar.
Representation of musical performance “grammar” using probabilistic graphical models
Authors: Ren Gang , Wen Zhe , Yang Xuchen , Shu Cheng , Ke Fangyu , Bocko Mark
Published: November 2013

As a versatile data modeling tool, probabilistic graphical model can be applied to model the complex dependency structures encoded in the contextual “grammar” of music performance. The musical performance grammar here refers to the relational structures of the sonic features extracted from music performances. In the existing literature, the data structure of musical expressive grammar is usually modeled as rule list, following the grammatical format of natural language processing applications. In this work, we apply the representation format of probabilistic graphical model to musical performance features to extend the conventional rule-list format. We choose probabilistic graphical model as an “upgraded” representation for two reasons. First, probabilistic graphical model provides enhanced representation capability of relational structures. This feature enables us to model the complex dependency structure that the conventionally rule list cannot handle. Second, the graphical format of probabilistic graphical model provides an intuitive human-data interface and allows in-depth data visualization, analysis, and interaction. We include the representation and analysis examples of musical performance grammar obtained from both manual analysis and automatic induction. We also implemented interpretation tools that interface the rule-list format and the probabilistic graphical model format to enable detailed comparison with existing results of musical performance analysis.
Transient nonlinear acoustical holography
Authors: Jing Yun , Cannata Jonathan
Published: November 2013

This paper presents our recent work on transient nonlinear acoustical holography. A higher order stepping algorithm is first introduced, which is shown to be significantly more accurate and efficient than the original one (Evaluation of a wave-vector-frequency-domain method for nonlinear wave propagation, Jing et al., J. Acoust. Soc. Am. 129, 32) through systematic numerical study. Underwater experimental results from a highly focused transducer will be presented here to show the validity of the model. Both linear and nonlinear, forward and backward projection of the acoustic field are conducted. While linear acoustical holography is shown to produce erroneous results, good agreement is found between our nonlinear model and the experiment.
Possibilities of tomography system prototype using third-order acoustic nonlinear effects
Authors: Burov Valentin A. , Kryukov Roman V. , Shmelev Andrey A. , Zotov Dmitry I. , Rumyantseva Olga D.
Published: November 2013

Third-order nonlinear acoustical tomography is very important for medical diagnostics, because it will provide information on the new and unexplored quantity—third-order nonlinear acoustical parameter. A prototype of the tomography system for reconstructing the distributions of the acoustic nonlinear parameters is developed in our group on the basis of effect of nonlinear noncollinear interaction of three primary waves. Application of coded primary signals with further correlation processing of a detected signal at combination frequencies makes it possible to reconstruct the complete image of an object using three transmitters and one receiver. Third-order effects are born from two competing processes—the pure third order interaction (informational for diagnostic purposes) and the twofold interaction of the second order (interfering). To explore the application boundaries of the third-order nonlinear acoustical tomography, these two competing processes are considered in details. Two cases are compared. In the first case, the interaction takes place between two broadband coded signals and one monochromatic signal. In the second case, all three primary signals are broadband coded; then, amplitude of the interfering part of the signal is smaller. Moreover, in this case, the possibility of reconstructing the spatial distribution of the second and third-order nonlinear acoustical parameters arises due to the reciprocity principle generalized on the nonlinear scattering processes.
Second-harmonic generation in shear wave beams with different polarizations
Authors: Spratt Kyle S. , Ilinskii Yurii A. , Zabolotskaya Evgenia A. , Hamilton Mark F.
Published: November 2013

A parabolic equation describing the propagation of collimated shear wave beams in isotropic elastic solids was derived by Zabolotskaya [Sov. Phys. Acoust. 32, 296–299 (1986)], and was seen to contain both cubic and quadratic nonlinear terms at leading order. While second-order nonlinear effects vanish for the quasi-planar case of linearly-polarized shear wave beams, the importance of quadratic nonlinearity for more complicated polarizations is not yet well understood. The current work investigates the significance of quadratic nonlinearity by considering second-harmonic generation in shear wave beams generated by a certain class of source polarizations that includes such cases as radial and torsional polarization, among others. Corresponding to such beams with Gaussian amplitude shading, analytic solutions are derived for the propagated beam at the source frequency and the second harmonic. Diffraction characteristics are discussed, and special attention is paid to the relationship between the source polarization of the beam and the polarization of the subsequently generated second harmonic. Finally, suggestions are made for possible experiments that could be performed in tissue phantoms, exploiting the theoretical results of this work. [Work supported by the ARL:UT McKinney Fellowship in Acoustics.]
A new look at the matched filter
Authors: Sullivan Edmund J. , Kelly James G.
Published: November 2013

The matched filter is well known as the optimal linear detector. It is generally used in threshold tests, which depend only on its maximum value. However, it is usually used as an estimator, an example being the case of range determination in the active sonar problem. But even in this case, only its peak value is used. Here, we look at what we refer to as the “complete” matched filter. By examining the full output of the matched filter we show that it is closely related to the deconvolution problem, which is not a detector but an estimator. Further, we show that for the case of a linear chirp (LFM) signal, the full matched filter and the deconvolution problem are essentially identical, the difference being in the power spectrum of the signal. The more the signal power spectrum deviates from whiteness, the greater the difference between the two, even if the time-bandwidth product of the signal remains the same. Moreover, we show that the LFM signal is an optimal signal for the deconvolution problem since it minimizes the variance of the estimate.
An alternative method for the estimation of underwater acoustic signal coherence
Authors: Dzieciuch Matthew , Worcester Peter
Published: November 2013

The estimator-correlator is the optimal method for measuring the travel-time of a scattered underwater tomographic acoustic signal. The method increases the signal-to-noise ratio at some cost in resolution when the signal and noise covariances are known. The noise covariance is easily measured when the signal is not present. The signal covariance may not be known but can be estimated as well. The procedure is to parameterize the signal covariance and find the maximum output signal-to-noise ratio of the estimator-correlator while varying the signal covariance parameters. Following Flatte et al., the path integral model of signal covariance is R = exp{ -(Δt/Tc)2 + (Δf/Bc)2 + (Δz/Dc)2}. Thus, a simple search over coherence time, Tc, coherence bandwidth, Bc, and coherence depth, Dc, produces estimates of those parameters. Application of this technique with data from three recent tomographic experiments will demonstrate its efficacy. Time coherence was measured during the 2009 Philippine Sea Experiment at 250 Hz and 190 km range. Vertical coherence was measured during the 2010 Philippine Sea experiment at 250 Hz and at ranges from 120 to 450 km. Horizontal coherence was measured in the North Pacific at 75 Hz and 3500 km range.
Evaluation of frequency characteristics of shear waves produced by unfocused and focused beams
Authors: Urban Matthew W. , Amador Carolina , Zhao Heng , Lee Mingu , Shim Hwan , Chen Shigao , Greenleaf James F.
Published: November 2013

Measurements of viscoelasticity with shear wave velocity dispersion requires measurements over a large bandwidth. In this study, we explored the parameters that modulate the frequency characteristics of shear waves induced using radiation force push beams. We used a Verasonics ultrasound scanner equipped with a linear array transducer. We performed measurements of shear wave motion induced using both focused and unfocused ultrasound beams. Measurements were made in elastic phantoms with shear moduli of 1, 4, and 16 kPa. The number of elements used for the unfocused beams were varied from 8 to 24, and for the focused beams from 16 to 128. The shear wave motion was tracked using plane wave imaging, and a one-dimensional autocorrelation algorithm applied to the acquired in-phase/quadrature data. At each pixel we calculated the fast Fourier transform of the data and found the center frequency, center-of-gravity, and −3 dB bandwidth. We compared the frequency characteristics from the different push beams. The frequency characteristics were found to be spatially variant and dependent on the number of elements used as well as the shear modulus of the medium. The center frequency, center-of-gravity, and the bandwidth were found to be correlated to one another, and strongly associated with the stiffness of the medium.
Using equilibrium equation constraints to obtain precise lateral displacement estimates in ultrasound imaging
Authors: Babaniyi Olalekan A. , Barbone Paul E. , Oberai Assad A.
Published: November 2013

Ultrasound elasticity imaging, whether based on radiation force, quasistatic deformation, or other means, depends upon using ultrasound to measure tissue motion. Ultrasound image data with standard beamforming can provide very precise measurements of soft tissue displacement in the axial direction, i.e., in the direction of the ultrasound beam. Lateral (and elevational) displacement estimates are relatively noisy. The authors describe a new processing method designed to estimate a precise and accurate 2D full displacement vector field from accurate measurements of a single component, and a noisy measurement of a second component. The proposed variational approach finds the displacement field that best fits the data, but that satisfies Navier's equation locally. The equilibrium equation is automatically relaxed along internal interfaces in the material, which need not be identified beforehand. In this way, the method accommodates piecewise constant material property distributions without knowing in advance where the properties change. The iterative implementation for plane stress incompressible elasticity converges in 3–10 iterations. [Authors gratefully acknowledge funding from NSF and NIH (NSF Grant No. 50201109; NIH NCI-R01CA140271).]
Approximate analytical models for cylindrical shear wave propagation in viscoelastic media
Authors: Yang Yiqun , Urban Matthew W. , Qiang Bob , McGough Robert J.
Published: November 2013

Improved approximate frequency domain expressions are derived for cylindrical shear wave propagation in viscoelastic media. These expressions extend prior results that describe cylindrical wave propagation in lossless media. Previously, an analytical expression for a cylindrical wave was obtained in terms of a Hankel function and a large argument approximation was applied to the result. A leading frequency-dependent term was then treated as a constant with respect to frequency. In the improved expression, the frequency-dependence of the leading term is retained. For lossless media, the leading term is a fractional integrator, and for viscoelastic media, the leading term is either a fractional integrator or an integer-order integrator, depending on the frequency range. The lossless and the viscoelastic models are evaluated in the frequency domain for simplified source geometries and compared to numerical results. The comparison shows that the agreement between the analytical and the numerical models is excellent. Implications for time-domain calculations in viscous media will also be discussed. [This work was supported in part by NIH Grant Nos. R01 EB012079 and R01 DK092255.]
Computer modeling as teaching tool in underwater acoustics
Authors: Isakson Marcia J.
Published: November 2013

One of the challenges of teaching acoustics is to bridge the gap between theory and application. However, laboratory experiments are often too difficult or costly particularly for large-scale phenomena such as ray bending in ocean acoustics. Computer modeling is a low cost, easily accessible way for students to visualize acoustic phenomena without the overhead of laboratory experiments. In the underwater acoustics course at the University of Texas at Austin, students develop an acoustic modeling suite throughout the course culminating in a code to solve the sonar equation for a target in a shallow water environment. Beginning with simple attenuation, students model rays bending due to sound speed profiles, modes, both propagating and leaky, reverberation, target scattering, array steering, and signal processing. Each component builds on previous code and, at the end of the course, the student has a coherent collection of underwater acoustic modeling tools.
Passive acoustic monitoring for marine mammals during Navy explosives training events off the coast of Virginia Beach, Virginia
Authors: Hotchkin Cara F. , Shoemaker Mandy , Kumar Anurag , Hager Carl , MacDuffee David , Nissen Jene , Filipowicz Ronald
Published: November 2013

Navy training events involving the use of explosives pose a potential threat to marine mammals. This study used passive acoustic and visual monitoring data to evaluate marine mammals’ behavioral responses to noise from explosive events. Monitoring was conducted during five training events in the Virginia Capes (VACAPES) Range Complex during August/September of 2009–2012. Passive acoustic monitoring methods ranged from a single hydrophone to an array of sonobuoys monitored in real time. Visual monitoring effort over the five events totaled approximately 34 h (day before events: 10.1 h; days of events: 22.3 h; day after events: 1.5 h), yielding a total of 27 marine mammal sightings. Approximately 54 h of acoustic data were collected before, during, and after the five events. Behavioral changes were evaluated based on analysis of vocalizations detected before, during, and after explosions and concurrent data from visual sightings. For time periods with both visual and acoustic monitoring data, detection methods were compared to evaluate effectiveness. Continuing use and evaluation of both visual and passive acoustic methods for monitoring of explosive training events will improve our knowledge of potential impact resulting from explosive events and help improve management and conservation of marine mammals.
Monitoring of marine mammal occurrence and acoustic behaviors in relation to mid-frequency active sonar using autonomous recorders deployed off the undersea warfare training range, Florida
Authors: Norris Thomas F. , Oswald Julie , Yack Tina M. , Ferguson Elizabeth , Kumar Anurag , Nissen Jene , Bell Joel
Published: November 2013

Passive acoustic data were collected from nine Marine Autonomous Recording Units (MARUs) deployed 60–150 km in an area that coincides with the U.S. Navy’s planned Undersea Warfare Training Range (USWTR) off Jacksonville FL. MARUs were deployed for 26 days during fall 2009, and 37 days in winter 2009–2010. Data were manually reviewed for marine mammal vocalization events, man-made noise, and mid-frequency active sonar events, which were logged using Triton software. Seasonal and diel patterns were characterized qualitatively. Patterns and probabilities of vocalization events by species, or species groups, were related to sonar events. Vocalizations were detected for minke whales, North Atlantic right whales, sei whales, humpback whales, sperm whales, the blackfish group, and delphinids. Minke whale pulse-trains occurred almost continuously during the winter deployment but were absent in fall. Right whale events occurred mostly during winter at shallow-water sites, but unexpectedly were also detected at deep-water sites. Sperm whale events occurred exclusively near the continental shelf break and exhibited a strong diel pattern. Minke whale events had a strong negative relationship with sonar events. These results provide an initial assessment of marine mammal occurrence within the Navy’s planned USWTR, and provide new information on vocalization events in relation to sonar.
Behavioral responses of California sea lions (Zalophus californianus) to controlled exposures of mid-frequency sonar signals
Authors: Houser Dorian S. , Martin Stephen W. , Finneran James J.
Published: November 2013

Acoustic dose-response functions can be used to explore the relationship between anthropogenic noise exposure and changes in marine mammal behavior. Fifteen sea lions participated in a controlled exposure study to determine the relationship between the received sound pressure level (SPL) of a mid-frequency sonar signal (1-s duration, 3250-3450 Hz) and behavioral deviations from a trained behavior. Sea lions performed 10 control trials followed by 10 exposure trials within an open-water enclosure. Acoustic playbacks occurred once during each exposure trial when the sea lion crossed the middle of the enclosure. Received levels, ranging from 125 to 185 dB re 1 μPa (rms) SPL, were randomly assigned but were consistent across all trials for each individual. Blind scoring of behavioral responses was performed for all trials. A canonical correlation analysis indicated that cessation of the trained behavior, haul-out, a change in respiration rate, and prolonged submergence were reliable response indicators. Sea lions showed both an increased responsiveness and severity of response with increasing received SPL. No habituation to repeated exposures was observed, but age was a significant factor affecting the dose-response relationship. Response patterns and factors affecting behavioral responses were different from those observed in bottlenose dolphins and are indicative of species-specific sensitivities.
Ultrasound-mediated stimulation of nanoparticles for therapeutic applications
Authors: Porter Tyrone M.
Published: November 2013

Ultrasound has the unique capability to change the pressure and temperature of tissue in a noninvasive and highly localized manner. Consequently, ultrasound is an attractive tool for enhancing the delivery of drugs to targeted cells and tissues. This talk will review a variety of stimuli-responsive drug carriers (i.e., liposomes, nanoparticles, emulsions, etc.) and the role of ultrasound in facilitating transport and drug delivery.