bluuebunny/crossref_metadata_2025 huggingface dataset:
An improved method for direct impedance deduction of a locally reacting ground
Authors: Tong Bao N. , Li Kai Ming
Published: October 2014

An accurate deduction of the acoustic impedance of a locally reacting ground depends on a precise measurement of sound fields at short-ranges. However, measurement uncertainties exists in both the magnitude and the phase of the acoustic transfer function. By using the standard method, accurate determination of the acoustic impedance can be difficult when the measured phases become unreliable in many outdoor conditions. An improved technique, which relies only on the magnitude information, has been developed. A minimum of two measurements at two source/receiver configurations are needed to determine the acoustic impedance. Even in the absence of measurement uncertainties, a more careful analysis suggests that a third independent measurement is often needed to give an accurate solution. When experimental errors are inevitably introduced, a selection of optimal geometry becomes necessary to reduce the sensitivity of the deduced impedance to small variations in the data. A graphical method is provided which offers greater insight into the deduction of impedance and a downhill simplex algorithm has been developed to automate the procedure. Physical constraints are applied to limit the search region and to eliminate the rogue solutions. Several case studies using indoor and outdoor data are presented to validate the proposed technique.
Space-time correlation of acoustic signals in a turbulent atmosphere
Authors: Ostashev Vladimir E. , Wilson D. Keith , Collier Sandra , Cheinet Sylvain
Published: October 2014

Scattering by atmospheric turbulence diminishes the correlation, in both space and time, of acoustic signals. This decorrelation subsequently impacts beamforming, averaging, and other techniques for enhancing signal-to-noise ratio. Space-time correlation can be measured directly with a phased microphone array. In this paper, a general theory for the space-time correlation function is presented. The atmospheric turbulence is modeled using the von Karman spatial spectra of temperature and wind velocity fluctuations and locally frozen turbulence (i.e., the Taylor’s frozen turbulence hypothesis with convection velocity fluctuations). The theory developed is employed to calculate and analyze the spatial and temporal correlation of acoustic signals for typical regimes of an unstable atmospheric boundary layer, such as mostly cloudy or sunny conditions with light, moderate, or strong wind. The results obtained are compared with available experimental data.
Analysis of wind noise reduction by semi-porous fabric domes
Authors: Collier Sandra L. , Raspet Richard , Noble John M. , Alberts W. C. Kirkpatrick , Webster Jeremy
Published: October 2014

For low frequency acoustics, the wind noise contributions due to turbulence may be divided into turbulence–sensor, turbulence–turbulence, and turbulence–mean shear interactions. Here, we investigate the use of a semi-porous fabric dome for wind noise reduction in the infrasound region. Comparisons are made between experimental data and theoretical predictions from a wind noise model [Raspet, Webster, and Naderyan, J. Acoust. Soc. Am. 135, 2381 (2014)] that accounts for contributions from the three turbulence interactions.
Faster frequency sweep methods for structural vibration and acoustics analyses
Authors: Wu Kuangcheng , Nguyen Vincent
Published: October 2014

The design of large, complex structures typically requires knowledge of the mode shape and forced response near major resonances to ensure deflection, vibration, and the resulting stress are kept below acceptable levels, and to guide design changes where necessary. Finite element analysis (FEA) is commonly used to predict Frequency Response Functions (FRF) of the structure. However, as the complexity and detail of the structure grows, the system matrices, and the computational resources needed to solve them, get large. Furthermore, the need to use small frequency steps to accurately capture the resonant response peaks can drive up the number of FRF calculations required. Thus, the FRF calculation can be computationally expensive for large structural systems. Several approaches have been proposed that can significantly accelerate the overall process by approximating the frequency dependent response. Approximation approaches based on Krylov Galerkin Projection (KGP) and Pade calculate the forced response at only a few frequencies, then use the response and its derivatives to reconstruct the FRF in-between the selected direct calculation points. This paper first validates the two approaches with analytic solutions for a simply supported plate, and then benchmarks several numerical examples to demonstrate the accuracy and efficiency of the new approximate methods.
Waves in continua with extreme microstructures
Authors: Barbone Paul E.
Published: October 2014

The effective properties of a material may be generally defined as those that describe the limiting case where the wavelength of propagation is infinite compared to the characteristic scale of the microstructure. Generally, the limit of vanishingly small microstructural scale in a heterogeneous elastic medium results in an effective homogeneous medium that is again elastic. We show that for materials with extreme microstructures, the limiting effective medium can be quite exotic, including polar materials, or multiphase continuum. These continuum models naturally give rise to unusual effective properties including negative or anisotropic mass. Though unusual, these properties have straightforward interpretations in terms of the laws of classical mechanics. Finally, we discuss wave propagation in these structures and find dispersion curves with multiple branches.
Energy flow models for the out-of-plane vibration of horizontally curved beams
Authors: Kil Hyun-Gwon , Seo Seonghoon , Hong Suk-Yoon , Lee Chan
Published: October 2014

The purpose of this work is to develop energy flow models to predict the out-of-plane vibration of horizontally curved beams in the mid- and high-frequency range. The dispersion relations of waves are approximately separated into relations to the propagation of flexural waves and torsional waves generating the out-of-plane vibration of the horizontally curved beams with Kirchhoff-Love hypotheses. The energy flow models are based on the energy governing equations for the flexural waves and the torsional waves propagating in the curved beams. Those equations are driven to predict the time- and locally space-averaged energy density and intensity in the curved beams. Total values for the energy density and the intensity as well as contributions of each type of waves on those values are predicted. A verification of the energy flow models for the out-of-plane vibration of the horizontally curved beams is performed by comparing the energy flow solutions for the energy density and the intensity with analytical solutions evaluated using the wave propagation approach. The comparison shows that the energy flow models can be effectively used to predict the out-of-plane vibration of the horizontally curved beams in the mid- and high-frequency range.
Structural–acoustic optimization of a pressurized, ribbed aircraft panel
Authors: Shepherd Micah R. , Hambric Stephen A.
Published: October 2014

A method to reduce the noise radiated by a ribbed, aircraft panel excited by turbulent boundary layer flow is presented. To compute the structural-acoustic response, a modal approach based on finite element/boundary element analysis was coupled to a turbulent boundary flow forcing function. A static pressure load was also applied to the panel to simulate cabin pressurization during flight. The radiated sound power was then minimized by optimizing the horizontal and vertical rib location and rib cross section using an evolutionary search algorithm. Nearly 10 dB of reduction was achieved by pushing the ribs to the edge of the panel, thus lowering the modal amplitudes excited by the forcing function. A static constraint was then included in the procedure using a low-frequency dynamic calculation to approximate the static response. The constraint limited the amount of reduction that was achieved by the optimizer.
A physical figure model of tongue muscles
Authors: Hirayama Makoto J.
Published: October 2014

To help understanding tongue shape and motions, a physical figure model of tongue muscles using viscoelastic material of urethane rubber gel were made by improving previous models. Compare to previous shape tongue models that had been made and presented, the new model is constructed from tongue body (consisting of Transversus linguae, Verticalis linguae, Longitudinalis linguae superior, and Longitudinalis linguae inferior), and individual extrinsic tongue muscles (consisting of Genioglossus anterior, Genio glossus posterior, Hyoglossus, Styloglossus, and Palatoglossus) parts. Therefore, each muscle’s shape, starting and ending points, and relation to other muscles and organs inside mouth are more understandable than previous ones. As the model is made from viscoelastic material similar to human skin, reshaping and moving tongue are possible by pulling or pushing some parts of the tongue muscle by hand, that is, tongue shape and motion simulations by hand can be done. The proposed model is useful for speech science education or a future speaking robot using realistic speech mechanism.
Tongue width at rest versus tongue width during speech: A comparison of native and non-native speakers
Authors: Kanada Sunao , Wilson Ian
Published: October 2014

Most pronunciation researchers do not focus on the coronal view. However, it is also important to observe because the tongue is hydrostatic. We believe that some pronunciation differences between native speakers and second-language (L2) speakers could be due to differences in the coronal plane. Understanding these differences could be a key to L2 learning and modeling. It may be beneficial for pedagogical purposes and the results of this research may contribute to the improvement of pronunciation of L2 English speakers. An interesting way to look at native and L2 articulation differences is through the pre-speech posture and inter-speech posture (ISP—rest position between sentences). In this research, we compare native speakers to L2 speakers. We measure how different those postures are from the median position of the tongue during speech. We focus on movement of a side tongue marker in the coronal plane, and we normalize for speaker size. We found that the mean distance from pre-speech posture to speech posture is shorter for native English speakers (0.95 mm) than for non-native English speakers (1.62 mm). So, native speakers are more efficient in their pre-speech posture. Results will also be shown for distances from ISP to speech posture.
Intraglottal velocity and pressure measurements in a hemilarynx model
Authors: Oren Liran , Khosla Sid , Gutmark Ephraim
Published: October 2014

Determining the mechanisms of self-sustained oscillation of the vocal folds requires characterization of intraglottal aerodynamics. Since most of the intraglottal aerodynamics forces cannot be measured in a tissue model of the larynx, most of the current understanding of vocal fold vibration mechanism is derived from mechanical, analytical, and computational models. In the current study, intraglottal pressure measurements are taken in a hemilarynx model and are compared with pressure values that are computed form simultaneous velocity measurements. The results show that significant negative pressure is formed near the superior aspect of the folds during closing, which is in agreement with previous measurements in a hemilarynx model. Intraglottal velocity measurements show that the flow near the superior aspect separates from the glottal wall during closing and may develop into a vortex, which further augments the magnitude of the negative pressure. The intraglottal pressure distributions are computed by solving the pressure Poisson equation using the velocity field measurements and show good agreement with the pressure measurements. The match between the pressure computations and the pressure measurements validates the technique, which was also used in previous study to estimate the intraglottal pressure distribution in a full larynx model.
An airflow examination of the Czech trills
Authors: Komova Ekaterina , Howson Phil
Published: October 2014

Previous studies have suggested that there is a difference between the Czech trills /r ̝/ and /r/ with respect to the airflow required to produce each trill. This study examines this question using an airflow meter. Five speakers of Czech produced /r ̝/ and /r/ in the real words řád “order,” pařát “talon,” tvař “face,” rád “like,” paráda “great,” and tvar “shape.” Airflow data were recorded using Macquirer. The data indicate a higher airflow during the production of /r ̝/ compared to /r/. /r ̝/ was produced with approximately 3 l/s more than /r/. The increased airflow is necessary to cross the boundary of laminar flow into turbulent flow and supports previous findings that /r ̝/ is produced with breathy voice, which facilities trilling during frication. The data also suggests that one of the factors that makes the plain trill /r/ difficult to produce is that the airflow required to produce a sonorous trill is tightly constrained. The boundaries between trill production and the production of frication are only a few l/s apart and thus requires careful management of the laryngeal mechanisms, which control airflow.
An electroglottography examination of fricative and sonorous segments
Authors: Howson Phil
Published: October 2014

It has been previously suggested that fricative production is marked by a longer glottal opening as compared to sonorous segments. The present study uses electroglottography (EGG) and acoustic measurements to test this hypothesis by examining the activity of the vocal cords during the articulation of fricative and sonorant segments of English and Sorbian. An English and a Sorbian speakers' extended individual productions of the phonemes /s, z, ʃ, ʒ, m, n, r, l, a/ and each phoneme in the context #Ca were recorded. The open quotient was calculated using MATLAB. H1-H2 measures were taken at 5% into the vowel following each C and at 50% into the vowel. The results indicate that the glottis is open longer during the production of fricatives than for sonorous segments. Furthermore, the glottis is slightly more open for the production of nasals and liquids than it is for vowels. These results suggest that a longer glottal opening facilitates the increased airflow required to produce frication. This contrasts previous analyses which suggested that frication is primarily achieved through a tightened constriction. While a tighter constriction may be necessary, the increased airflow velocity produced by a longer glottal opening is critical for the production of frication.
Acoustic correlates of bilingualism: Relating phonetic production to language experience and attitudes
Authors: Law Wai Ling , Francis Alexander L.
Published: October 2014

Researchers tend to quantify degree of bilingualism according to age-related factors such as age of acquisition (Flege, et al. 1999, Yeni-Komshian, et al. 2000). However, previous research suggests that bilinguals may also show different degrees of accent and patterns of phonetic interaction between their first language (L1) and second language (L2) as a result of factors such as the quantity and quality of L2 input (Flege & Liu, 2001), amount of L1 vs. L2 use (Flege, et al. 1999), and attitude toward each language (Moyer, 2007). The goal of this study is to identify gradient properties of speech production that can be related to gradient language experience and attitudes in a bilingual population that is relatively homogeneous in terms of age-related factors. Native Cantonese-English bilinguals living in Hong Kong produced near homophones in both languages under conditions emphasizing one language or the other on different days. Acoustic phonetic variables related to phonological inventory differences between the two languages, including lexical tone/stress, syllable length, nasality, fricative manner and voicing, release of stop, voice onset time, and vowel quality and length, will be quantified and compared to results from a detailed survey of individual speakers’ experience and attitudes toward the two languages.
Relative distances among English front vowels produced by Korean and American speakers
Authors: Yang Byunggon
Published: October 2014

This study examined the relative distances among English front vowels in a message produced by 47 Korean and American speakers from an internet speech archive in order to provide better pronunciation skills for Korean English learners. The Euclidean distances in the vowel space of F1 and F2 were measured among the front vowel pairs. The first vowel pair [i-ɛ] was set as the reference from which the relative distances of the other two vowel pairs were measured in percent in order to compare the vowel sounds among speakers of different vocal tract lengths. Results show that F1 values of the front vowels produced by the Korean and American speakers increased from the high front vowel to the low front vowel with differences among the groups. The Korean speakers generally produced the front vowels with smaller jaw openings than the American speakers did. Second, the relative distance of the high front vowel pair [i-ɪ] showed a significant difference between the Korean and American speakers while that of the low front vowel pair [ɛ-æ] showed a non-significant difference. Finally, the Korean speakers in the higher proficiency level produced the front vowels with higher F1 values than those in the lower proficiency level.
Moving source localization and tracking based on data
Authors: Yang Tsih C.
Published: October 2014

Matched field processing (MFP) was introduced sometimes ago for source localization based on the replica field for a hypothesized source location that best matches the acoustic data received on a vertical line array (VLA). A data-based matched-mode source localization method is introduced in this paper for a moving source, using mode wavenumbers and depth functions estimated directly from the data, without requiring any environmental acoustic information and assuming any propagation model to calculate the replica field. The method is in theory free of the environmental mismatch problem since the mode replicas are estimated from the same data used to localize the source. Besides the estimation error due to the approximations made in deriving the data-based algorithms, the method has some inherent drawbacks: (1) it uses a smaller number of modes than theoretically possible, since some modes are not resolved in the measurements, and (2) the depth search is limited to the depth covered by the receivers. Using simulated data, it is found that the performance degradation due to the above approximation/limitation is marginal compared with the original matched-mode source localization method. Certain aspects of the proposed method have previously been tested against data. The key issues are discussed in this paper.
Simultaneous localization of multiple vocalizing humpback whale calls in an ocean waveguide with a single horizontal array using the array invariant
Authors: Gong Zheng , Lee Sunwoong , Ratilal Purnima , Makris Nicholas C.
Published: October 2014

The array invariant method, previously derived for instantaneous range and bearing estimation of a broadband impulsive source in a horizontally stratified ocean waveguide [Lee and Makris, J. Acoust. Soc. Am. 119, 336–351 (2006)], is generalized to instantaneously and simultaneously localize multiple uncorrelated broadband noise sources that not necessarily impulsive in the time domain. In an ideal Pekeris waveguide, we theoretically show that source range and bearing can be instantaneously obtained from beam-time migration lines measured with a horizontal array through range and bearing dependent differences that arise between modal group speeds along the array. We also show that this theory is approximately valid in a horizontally stratified ocean waveguide. A transform, similar to the Radon transform, is employed to enable simultaneous localization of multiple uncorrelated broadband noise sources without ambiguity using the array invariant method. The method is now applied to humpback whale vocalization data from the Gulf of Maine 2006 Experiment for humpback whale ranges up to tens of kilometers, where it is shown that accurate bearing and range estimation of multiple vocalizing humpback whales can be simultaneously made with little computational effort.
Test for eigenspace stationarity applied to multi-rate adaptive beamformer
Authors: Quijano Jorge E. , Zurk Lisa M.
Published: October 2014

Array processing in the presence of moving targets is challenging since the number of stationary data snapshots required for estimation of the data covariance are limited. For experimental scenarios that include a combination of fast maneuvering loud interferers and quiet targets, the multi-rate adaptive beamformer (MRABF) can mitigate the effect of non-stationarity. In MRABF, the eigenspace associated to loud interferers is first estimated and removed, followed by application of adaptive beamforming techniques to the remaining, less variable, “target” subspace. Selection of the number of snapshots used for estimation of the interferer eigenspace is crucial in the operation of MRABF, since too few snapshots result in poor eigenspace estimation, while too many snapshots result in leakage of non-stationary interferer effects into the target subspace. In this work an eigenvector-based test for data stationarity, recently developed in the context of very large arrays with snapshot deficiency, is used as a quantitative method to select the optimal number of snapshots for the estimation of the non-stationary eigenspace. The approach is demonstrated with simulated and experimental data from the Shallow Water Array Performance (SWAP) experiment.
Localization of a high frequency source in a shallow ocean sound channel using frequency-difference matched field processing
Authors: Worthmann Brian , Song H. C. , Dowling David R.
Published: October 2014

Matched field processing (MFP) is an established technique for locating remote acoustic sources in known environments. Unfortunately, environment-to-propagation model mismatch prevents successful application of MFP in many circumstances, especially those involving high frequency signals. For beamforming applications, this problem was found to be mitigated through the use of a nonlinear array-signal-processing technique called frequency difference beamforming (Abadi et al. 2012). Building on that work, this nonlinear technique was extended to MFP, where Bartlett ambiguity surfaces were calculated at frequencies two orders of magnitude lower than the propagated signal, where the detrimental effects of environmental mismatch are much reduced. In the Kauai Acomms MURI 2011 (KAM11) experiment, underwater signals of frequency 11.2 kHz to 32.8 kHz were broadcast 3 km through a 106-m-deep shallow-ocean sound channel and were recorded by a sparse 16-element vertical array. Using the ray-tracing code Bellhop as the propagation model, frequency difference MFP was performed, and some degree of success was found in localizing the high frequency source. In this presentation, the frequency difference MFP technique is explained, and comparisons of this nonlinear MFP technique with conventional Bartlett MFP using both simulations and KAM11 experimental data are provided. [Sponsored by the Office of Naval Research.]
Transarctic acoustic telemetry
Authors: Song Hee-Chun , Mikhalvesky Peter , Baggeroer Arthur
Published: October 2014

On April 9 and 13, 1999, two Arctic Climate Observation using Underwater Sound (ACOUS) tomography signals were transmitted from a 20.5-Hz acoustic source moored at the Franz Victoria Strait to an 8-element, 525-m vertical array at ice camp APLIS in the Chukchi Sea at a distance of approximately 2720 km. The transmitted signal was a 20-min long, 255-digit m-sequence that can be treated as a binary-phase shift-keying communication signal with a data rate of 2 bits/s. The almost error-free performance using either spatial diversity (three elements) for a single transmission or temporal diversity (two transmissions) with a single element demonstrates the feasibility of ice-covered trans-Arctic acoustic communications.
Performance of adaptive multichannel decision-feedback equalization in the simulated underwater acoustic channel
Authors: Sheng Xueli , Fan Lina , Song Aijun , Badiey Mohsen
Published: October 2014

Adaptive multichannel decision feedback equalization [M. Stojanovic, J. Catipovic, and J. G. Proakis, J. Acoust. Soc. Am. 94, 1621–1631 (1993)] is widely adopted to address the severe inter-symbol interference encountered in the underwater acoustic communication channel. In this presentation, its performance will be reported in the simulated communication channel provided by a ray-based acoustic model, for different ocean conditions and source-receiver geometries. The ray model uses the Rayleigh parameter to prescribe the sea surface effects on the acoustic signal. It also supports different types of sediment. The ray model output has been compared with the experimental data and shows comparable results in transmission loss. We will also compare against the performance of multichannel decision feedback equalization supported by existing ray models, for example, BELLHOP.
Space-time block code with equalization technology for underwater acoustic channels
Authors: Wang Chunhui , Sheng Xueli , Fan Lina , Lu Jia , Dong Weijia
Published: October 2014

In order to combat the effects of multipath interference and fading for underwater acoustic (UWA) channels, this paper investigates a scheme of the combination of space-time block code (STBC) and equalization technology. STBC is used in this scheme to reduce the effects of fading for the UWA channels, then equalization technology is used in this scheme to mitigate intersymbol interference. The performance of the scheme is analyzed with Alamouti space-time coding for the UWA channels. Our simulations indicate that the combination of STBC and equalization technology provides lower bit error rates.
Adaptive passive fathometer processing of surface-generated noise received by Nested array
Authors: Kim Junghun , Choi Jee W.
Published: October 2014

Recently, a passive fathometer technique using surface-generated ambient noise has been applied to the estimate of bottom profile. This technique performs the beamforming of ambient noise received by a vertical line array to estimate the sub-bottom layer structure as well as water depth. In the previous works, the surface noise signal processing was performed with equally spaced line arrays and the main topic of the research was the comparison of the results estimated using several beamforming techniques. In this talk, the results estimated from the ambient noise received by the Nested vertical line array (called POEMS) which consists of the total 24-elments and four sub-bands are presented. The measurements were made on the eastern coast (East Sea) of Korea. Four kinds of beamforming algorithms are applied to each sub-band and also, nested array processing combining each sub-band signal was performed to obtain the best result. The results are compared to the bottom profiles from the chirp sonar. [This research was supported by the Agency for Defense Development, Korea.]
Feasibility of low-frequency acoustic thermometry using deep ocean ambient noise in the Atlantic, Pacific, and Indian Oceans
Authors: Woolfe Katherine F. , Sabra Karim G.
Published: October 2014

Previous work has demonstrated the feasibility of passive acoustic thermometry using coherent processing of low frequency ambient noise (1–40 Hz) recorded on triangular hydrophones arrays spaced ~130 km and located in the deep sound channel. These triangular arrays are part of hydroacoustic stations of the International Monitoring System operated by the Comprehensive Nuclear Test Ban Treaty Organization (Woolfe et al., J. Acoust. Soc. Am. 134, 3983). To understand how passive thermometry could potentially be extended to ocean basin scales, we present a comprehensive study of the coherent components of low-frequency ambient noise recorded on five hydroacoustic stations located Atlantic, Pacific, and Indian Oceans. The frequency dependence and seasonal variability of the spatial coherence and directionality of the low-frequency ambient noise were systematically examined at each of the tested site locations. Overall, a dominant coherent component of the low-frequency noise was found to be caused by seasonal ice-breaking events at the poles for test sites that have line-of-sight paths to polar ice. These findings could be used to guide the placement of hydrophone arrays over the globe for future long-range passive acoustic thermometry experiments.
Vibrato parameterization
Authors: Beauchamp James W.
Published: October 2014

In an effort to improve the quality of synthetic vibrato many musical instrument tones with vibrato have been analyzed and frequency-vs-time curves have been parameterized in terms of a time-varying offset and a time-varying vibrato depth. Results for variable mean F0 and instrument are presented. Whereas vocal vibrato appears to sweep out the resonance characteristic of the vocal tract, as shown by amplitude-vs-frequency curves for the superposition of a range of harmonics, amplitude-vs-frequency curves for instruments are dominated by hysteresis effects that obscure their interpretation in terms of resonance characteristics. Nevertheless, there is a strong correlation between harmonic amplitude and frequency modulations. An effort is being made to parameterize this effect in order to provide efficient and expressive synthesis of vibrato tones with independent control of vibrato rate and tone duration.
Get real: Improving acoustic environments in video games
Authors: Lysoivanov Yuri
Published: October 2014

As processing power grows the push for realism in video games continues to expand. However, techniques for generating realistic acoustic environments in games have often been limited. Using examples from major releases, this presentation will take a historical perspective on interactive environment design, discuss current methods for modeling acoustic environments in games and suggest specific cases where acoustic expertise can provide an added layer to the interactive experience.
Twenty years of electronic architecture in the Hilbert Circle Theatre
Authors: Scarbrough Paul , Barbar Steve
Published: October 2014

In 1984, the Circle Theatre underwent a major renovation, transforming the original 3000 + seat venue into a 1780 seat hall with reclaimed internal volume dedicated to a new lobby and an orchestra rehearsal space. In 1996, a LARES acoustic enhancement system replaced the original electronic architecture system, and has been used in every performance since that time. We will discuss details of the renovation, the incorporation of the electronic architecture with other acoustical treatments, system performance over time, and plans for the future.
Analysis of room acoustical characteristics by plane wave decomposition using spherical microphone arrays
Authors: Jeon Jin Yong , Imran Muhammad , Lim Hansol
Published: October 2014

The room acoustical characteristics have been investigated in temporal and spatial structures of room impulse responses (IRs) at different audience positions in real halls. The spherical microphone array of 32-channel is used for measurements process. Specular and diffusive reflections in IRs have been visualized in temporal domain with sound-field decomposition analysis. For plane wave decomposition, the spherical harmonics are used. The beamforming technique is also employed to make directional measurements and for the spatio-temporal characterization of sound field. The directional measurements by beamforming are performed for producing impulse responses for the different directions to characterize the sound. From the estimation of spatial characterization, the reflective surfaces of the hall are indicated as responsible for specular and diffusive reflections.
Amplitude shifts in the cochlear microphonics of Mongolian gerbils created by noise exposure
Authors: Kawai Shin , Riquimaroux Hiroshi
Published: October 2014

The Mongolian gerbil (Meriones unguiculatus) was used to evaluate effects of intense noise exposure on functions of the hair cells. Cochlear microphonics (CM) served an index to show functions of the hair cells. The purpose of this study was to verify which frequency was most damaged by noise exposure and examine relationships between the frequency and the animal’s behaviors. We measured growth and recovery of the temporal shifts in amplitude of CM. The CM was recorded from the round window. Test stimuli used were tone bursts (1–45 kHz in half octave step), with duration of 50 ms (5 ms rise/fall times). The subject was exposed to broadband noise (0.5 to 60 kHz) at 90 dB SPL for 5 minutes. Threshold shifts were measured for the testing tone bursts from immediately after the exposure up to 120 minutes after the exposure. Findings showed that reduction in CM amplitude was observed after the noise exposure. Especially, large reduction was produced in a frequency range of 22.4 kHz. However, little reduction was observed around a frequency range of 4 kHz.
Acoustic detection of migrating gray, humpback, and blue whales in the coastal, northeast Pacific
Authors: Guazzo Regina A. , Hildebrand John A. , Wiggins Sean M.
Published: October 2014

Many large cetaceans of suborder Mysticeti make long annual migrations along the California coast. A bottom-mounted hydrophone was deployed in shallow water off the coast of central California and recorded during November 2012 to September 2013. The recording was used to determine the presence of blue whales, humpback whales, and gray whales. Gray whale calls were further analyzed and the number of calls per day and per hour were calculated. It was found that gray whales make their migratory M3 calls at a higher rate than previously observed. There were also more M3 calls recorded at night than during the day. This work will be continued to study the patterns and interactions between species and compared with shore-based survey data.
Social calling behavior in Southeast Alaskan humpback whales (Megaptera novaeangliae): Communication and context
Authors: Fournet Michelle , Szabo Andrew R. , Mellinger David K.
Published: October 2014

Across their range humpback whales (Megaptera novaeangliae) produce a wide array of vocalizations including song, foraging vocalizations, and a variety of non-song vocalizations known as social calls. This study investigates the social calling behavior of Southeast Alaskan humpback whales from a sample of 299 vocalizations paired with 365 visual surveys collected over a three-month period on a foraging ground in Frederick Sound in Southeast Alaska. Vocalizations were classified using visual-aural analysis, statistical cluster analyses, and discriminant function analysis. The relationship between vocal behavior and spatial-behavioral context was analyzed using a Poisson log-linear regression (PLL). Preliminary results indicate that some call types were commonly produced while others were rare, and that the greatest variety of calling occurred when whales were clustered. Moreover, calling rates in one vocal class, the pulsed (P) vocal class, were negatively correlated with mean nearest-neighbor distance, indicating that P calling rates increased as animals clustered, suggesting that the use of P calls may be spatially mediated. The data further suggest that vocal behavior varies based on social context, and that vocal behavior trends toward complexity as the potential for social interactions increases. [Work funded by Alaska Whale Foundation and ONR.]
Seismic airgun surveys and vessel traffic in the Fram Strait and their contribution to the polar soundscape
Authors: Nieukirk Sharon L. , Klinck Holger , Mellinger David K. , Klinck Karolin , Dziak Robert P.
Published: October 2014

Low-frequency (<1 kHz) noise associated with human offshore activities has increased dramatically over the last 50 years. Of special interest are areas such as the Arctic where anthropogenic noise levels are relatively low but could change dramatically, as sea ice continues to shrink and trans-polar shipping routes open. In 2009, we began an annual deployment of two calibrated autonomous hydrophones in the Fram Strait to record underwater ambient sound continuously for one year at a sampling rate of 2 kHz. Ambient noise levels were summarized via long-term spectral average plots and reviewed for anthropogenic sources. Vessel traffic data were acquired from the Automatic Identification System (AIS) archive and ship density was estimated by weighting vessel tracklines by vessel length. Background noise levels were dominated by sounds from seismic airguns during spring, summer and fall months; during summer these sounds were recorded in all hours of the day and all days of a month. Ship density in the Fram Strait peaked in late summer and increased every year. Future increases in ship traffic and seismic surveys coincident with melting sea ice will increase ambient noise levels, potentially affecting the numerous species of acoustically active whales using this region.
Using the dynamics of mouth opening in echolocating bats to predict pulse parameters among individual Eptesicus fuscus
Authors: Kloepper Laura N. , Simmons James A. , Buck John R.
Published: October 2014

The big brown bat (Eptesicus fuscus) produces echolocation sounds in its larynx and emits them through its open mouth. Individual mouth-opening cycles last for about 50 ms, with the sound produced in the middle, when the mouth is approaching or reaching maximum gape angle. In previous work, the mouth gape-angle at pulse emission only weakly predicted pulse duration and the terminal frequency of the first-harmonic FM downsweep. In the present study, we investigated whether the dynamics of mouth opening around the time of pulse emission predict additional pulse waveform characteristics. Mouth angle openings for 24 ms before and 24 ms after pulse emission were compared to pulse waveform parameters for three big brown bats performing a target detection task. In general, coupling to the air through the mouth seems less important than laryngeal factors for determining acoustic parameters of the broadcasts. Differences in mouth opening dynamics and pulse parameters among individual bats highlight this relation. [Supported by NSF and ONR.]
Analysis of sound speed fluctuations in the Fram Strait near Greenland during summer 2013
Authors: Raghukumar Kaustubha , Colosi John A. , Worcester Peter F.
Published: October 2014

We analyze sound speed fluctuations in roughly 600 m deep polar waters from a recent experiment. The Thin-ice Arctic Acoustics Window (THAAW) experiment was conducted in the waters of Fram Strait, east of Greenland, during the summer of 2013. A drifting acoustic mooring that incorporated environmental sensors measured temperature and salinity over a period of four months, along a 500 km north-south transect. We examine the relative contributions of salinity-driven polar internal wave activity, and temperature/salinity variability along isopycnal surfaces (spice) on sound speed perturbations in the Arctic. Both internal-wave and spice effects are compared against the more general deep water PhilSea09 measurements. Additionally, internal wave spectra, energies, and modal bandwidth are compared against the well-known Garrett-Munk spectrum. Given the resurgence of interest in polar acoustics, we believe that this analysis will help parameterize sound speed fluctuations in future acoustic propagation models.
Waveform inversion of ambient noise cross-correlation functions in a coastal ocean environment
Authors: Zang Xiaoqin , Brown Michael G. , Williams Neil J. , Godin Oleg A. , Zabotin Nikolay A. , Zabotina Liudmila
Published: October 2014

Approximations to Green's functions have been obtained by cross-correlating concurrent records of ambient noise measured on near-bottom instruments at 5 km range in a 100 m deep coastal ocean environment. Inversion of the measured cross-correlation functions presents a challenge as neither ray nor modal arrivals are temporally resolved. We exploit both ray and modal expansion of the wavefield to address the inverse problem using two different parameterizations of the seafloor structure. The inverse problem is investigated by performing an exhaustive search over the relevant parameter space to minimize the integrated squared difference between computed and measured correlation function waveforms. To perform the waveform-based analysis described, it is important that subtle differences between correlation functions and Green's functions are accounted for. [Work supported by NSF and ONR.]
250-MHz quantitative acoustic microscopy for assessing human lymph-node microstructure
Authors: Rohrbach Daniel , Saegusa-Beecroft Emi , Yanagihara Eugene , Machi Junji , Feleppa Ernest J. , Mamou Jonathan
Published: October 2014

We employed quantitative acoustic microscopy (QAM) to measure acoustic properties of tissue microstructure. 32 QAM datasets were acquired from 2, fresh and 11, deparaffinized, 12-µm-thick lymph-node samples obtained from cancer patients. Our custom-built acoustic microscope was equipped with an F-1.16, 250-MHz transducer having a 160-MHz bandwidth to acquire reflected signals from the tissue and a substrate that intimately contacted the tissue. QAM images with a spatial resolution of 7 µm were generated of attenuation (A), speed of sound (SOS), and acoustic impedance (Z). Samples then were stained using hematoxylin and eosin, imaged by light microscopy, and co-registered to QAM images. The spatial resolution and contrast of QAM images were sufficient to distinguish tissue regions consisting of lymphocytes, fat cells and fibrous tissue. Average properties for lymphocyte-dominated tissue were 1552.6 ± 30 m/s for SOS, 9.53 ± 3.6 dB/MHz/cm for A, and 1.58 ± 0.08 Mrayl for Z. Values for Z obtained from fresh samples agreed well with those obtained from 12-µm sections from the same node. Such 2D images provide a basis for developing improved ultrasound-scattering models underlying quantitative ultrasound methods currently used to detect cancerous regions within lymph nodes. [NIH Grant R21EB016117.]
Detection of sub-micron lipid droplets using transmission-mode attenuation measurements in emulsion phantoms and liver
Authors: Kreider Wayne , Tabatabai Ameen , Maxwell Adam D. , Wang Yak-Nam
Published: October 2014

In liver transplantation, donor liver viability is assessed by the both the amount and type of fat present in the organ. General guidelines dictate that livers with more than 30% fat should not be transplanted; however, a lack of available donor organs has led to the consideration of livers with more fat. As a part of this process, it is desirable to distinguish micro-vesicular fat (< 1 µm droplets) from macro-vesicular fat (~10 µm droplets). A method of evaluating the relative amounts of micro- and macro-fat is proposed based on transmission-mode ultrasound attenuation measurements. For an emulsion of one liquid in another, attenuation comprises both intrinsic losses in each medium and excess attenuation associated with interactions between media. Using an established coupled-phase model, the excess attenuation associated with a monodisperse population of lipid droplets was calculated with physical properties representative of both liver tissue and dairy products. Calculations predict that excess attenuation can exceed intrinsic attenuation and that a well-defined peak in excess attenuation at 1 MHz should occur for droplets around 0.8 µm in diameter. Such predictions are consistent with preliminary transmission-mode measurements in dairy products. [Work supported by NIH grants EB017857, EB007643, EB016118, and T32 DK007779.]
Experimental comparison of methods for measuring backscatter coefficient using single element transducers
Authors: Stiles Timothy , Selep Andrew
Published: October 2014

The backscatter coefficient (BSC) has promise as a diagnostic aid. However, measurements of the BSC of soft-tissue mimicking materials have proven difficult; results on the same samples by various laboratories have up to two orders of magnitude difference. This study compares methods of data analysis using data acquired from the same samples using single element transducers, with a frequency range of 1 to 20 MHz and pressure focusing gains between 5 and 60. The samples consist of various concentrations of milk in agar with scattering from glass microspheres. Each method utilizes a reference spectrum from a planar reflector but differ in the diffraction and attenuation correction algorithms. Results from four methods of diffraction correction and three methods of attenuation correction are compared to each other and to theoretical predictions. Diffraction correction varies from no correction to numerical integration of the beam throughout the data acquisition region. Attenuation correction varies from limited correction for the attenuation up to the start of the echo acquisition window, to correcting for attenuation within a numerical integration of the beam profile. Results indicate the best agreements with theory are the methods that utilize the numerical integration of the beam profile.
Acoustic radiation force due to nonaxisymmetric sound beams incident on spherical viscoelastic scatterers in tissue
Authors: Treweek Benjamin C. , Ilinskii Yurii A. , Zabolotskaya Evgenia A. , Hamilton Mark F.
Published: October 2014

The theory for acoustic radiation force on a viscoelastic sphere of arbitrary size in tissue was extended recently to account for nonaxisymmetric incident fields [Ilinskii et al., POMA 19, 045004 (2013)]. A spherical harmonic expansion was used to describe the incident field. This work was specialized at the spring 2014 ASA meeting to focused axisymmetric sound beams with various focal spot sizes and a scatterer located at the focus. The emphasis of the present contribution is nonaxisymmetric fields, either through moving the scatterer off the axis of an axisymmetric beam or through explicitly defining a nonaxisymmetric beam. This is accomplished via angular spectrum decomposition of the incident field, spherical wave expansions of the resulting plane waves about the center of the scatterer, Wigner D-matrix transformations to express these spherical waves in a coordinate system with the polar axis aligned with the desired radiation force component, and finally integration over solid angle to obtain spherical wave amplitudes as required in the theory. Various scatterer sizes and positions relative to the focus are considered, and the effects of changing properties of both the scatterer and the surrounding tissue are examined. [Work supported by the ARL:UT McKinney Fellowship in Acoustics.]
Quantifying mechanical heterogeneity of breast tumors using quantitative ultrasound elastography
Authors: Liu Tengxiao , Babaniyi Olalekan A. , Hall Timothy J. , Barbone Paul E. , Oberai Assad A.
Published: October 2014

Heterogeneity is a hallmark of cancer whether one considers the genotype of cancerous cells, the composition of their microenvironment, the distribution of blood and lymphatic microvasculature, or the spatial distribution of the desmoplastic reaction. It is logical to expect that this heterogeneity in tumor microenvironment will lead to spatial heterogeneity in its mechanical properties. In this study we seek to quantify the mechanical heterogeneity within malignant and benign tumors using ultrasound based elasticity imaging. By creating in-vivo elastic modulus images for ten human subjects with breast tumors, we show that Young’s modulus distribution in cancerous breast tumors is more heterogeneous when compared with tumors that are not malignant, and that this signature may be used to distinguish malignant breast tumors. Our results complement the view of cancer as a heterogeneous disease by demonstrating that mechanical properties within cancerous tumors are also spatially heterogeneous. [Work supported by NIH, NSF.]