bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of fluid medium flow and spatial temperature variation on acoustophoretic motion of microparticles in microfluidic channels
Authors: Liu Zhongzheng , Kim Yong-Joe
Published: October 2014

Current, state-of-the-art models of acoustophoretic forces, applied to microparticles suspended in fluid media inside microfluidic channels, and acoustic streaming velocities inside the microfluidic channels have been mainly derived with the assumption of “static” fluid media with uniform temperature distributions. Therefore, it has been challenging to understand the effects of “moving” fluid media and fluid medium temperature variation on acoustophoretic microparticle motion in the microfluidic channels. Here, a numerical modeling method to accurately predict the acoustophoretic motion of compressible microparticles in the microfluidic channels is presented to address the aforementioned challenge. In the proposed method, the Mass, Momentum, and Energy Conservation Equations and the State Equation are decomposed by using a perturbation method into the zeroth- to the second-order equations. Here, the fluid medium flow and temptation variation are considered in the zeroth-order equations and the solutions of the zeroth-order equations (i.e., the zeroth-order fluid medium velocities and temperature distribution) are propagated into the higher-order equations, ultimately affecting the second-order acoustophoretic forces and acoustic streaming velocities. The effects of the viscous fluid medium flow and the medium temperature variation on the acoustophoretic forces and the acoustic streaming velocities were then studied in this article by using the proposed numerical modeling method.
Chronotropic effect in rats heart caused by pulsed ultrasound
Authors: Coiado Olivia C. , O'Brien William D.
Published: October 2014

This study investigated the dependence of an increasing/decreasing sequence of pulse repetition frequencies (PRFs) on the chronotropic effect via the application of 3.5-MHz pulsed ultrasound (US) on the rat heart. The experiments were divided into three 3-month-old female rat groups (n = 4 ea): control, PRF increase and PRF decrease. Rats were exposed to transthoracic ultrasonic pulses at ~0.50% of duty factor at 2.0-MPa peak rarefactional pressure amplitude. For the PRF increase group, the PRF started lower than that of the rat’s heart rate and was increased sequentially in 1-Hz steps every 5 s (i.e., 4, 5, and 6 Hz) for a total duration of 15 s. For the PRF decrease group, the PRF started greater than that of the rat’s heart rate and was decreased sequentially in 1-Hz steps every 5 s (i.e., 6, 5, and 4 Hz). For the PRF decrease and control groups, the ultrasound application resulted in a significant negative chronotropic effect (~11%) after ultrasound exposure. However, for the PRF increase group, a significant but less decrease of the heart rate (~3%) was observed after ultrasound exposure. The ultrasound application caused a negative chronotropic effect after US exposure for increase/decrease US group. [Support: NIH Grant R37EB002641.]
Ultrasonic welding in orthopedic implants
Authors: Korkowski Kristi R. , Bigelow Timothy
Published: October 2014

A critical event in hip replacement is the occurrence of osteolysis. Cemented hip replacements most commonly use polymethylmethacrylate (PMMA), not as an adhesive but rather a filler to limit micromotion and provide stability. PMMA, however, contributes to osteolysis through both a thermal response during curing and implant wear debris. In order to mitigate the occurrence of osteolysis, we are exploring ultrasonic welding as a means of attachment. Weld strength was assessed using ex vivo bovine rib and femur bones. A flat end mill provided 20 site locations for insertion of an acrylonitrile butadiene styrene, ABS pin. Each location was characterized on topography, porosity, discoloration, and any other notable features. Each site was welded using a Branson Ultrasonic Welder 2000iw; 20 kHz, 1100 W. Machine parameters include weld force, weld time, and hold time. The bond strength was determined using a tensile tester. Tensile testing showed a negative correlation between porosity and bond strength. Further evaluation and characterization of bone properties to bond strength will enable appropriate selection of welding properties to ensure a superior bond.
Estimation of subsurface temperature profiles from infrared measurements during ultrasound ablation
Authors: Fosnight Tyler R. , Hooi Fong Ming , Colbert Sadie B. , Keil Ryan D. , Mast T. Douglas
Published: October 2014

Measurement of in situ spatiotemporal temperature profiles would be useful for developing and validating thermal ablation methods and therapy monitoring approaches. Here, finite difference and analytic solutions to Pennes’ bio-heat transfer equation were used to determine spatial correlations between temperature profiles on parallel planes. Time delays and scale factors for correlated profiles were applied to infrared surface-temperature measurements to estimate subsurface temperatures. To test this method, exvivo bovine liver tissue was sonicated by linear image-ablate arrays with 1–6 pulses of 5.0 MHz unfocused (7.5 s, 64.4–92.0 W/cm2 in situ ISPTP) or focused (1 s, 562.7–799.6 W/cm2 in situ ISPTP, focus depth 10 mm) ultrasound. Temperature was measured on the liver surface by an infrared camera at 1 fps and extrapolated to the imaging/ablation plane, 3 mm below the surface. Echo decorrelation maps were computed from pulse-echo signals captured at 118 fps during 5.0 s rest periods beginning 1.1 s after each sonication pulse. Tissue samples were frozen at −80  °C, sectioned, vitally stained, imaged, and segmented for analysis. Estimated thermal dose profiles showed correspondence with segmented tissue histology, while thresholded temperature profiles corresponded with measured echo decorrelation. These results suggest utility of this method for thermal ablation research.
Implementation of a perfectly matched layer in nonlinear continuous wave ultrasound simulations
Authors: Zhao Xiaofeng , McGough Robert
Published: October 2014

FOCUS, the "Fast Object-Oriented C + + Ultrasound Simulator" (http://www.egr.msu.edu/~fultras-web), simulates nonlinear ultrasound propagation by numerically evaluating the Khokhlov–Zabolotskaya–Kuznetsov (KZK) equation. For continuous-wave excitations, KZK simulations in FOCUS previously required that the simulations extend over large radial distances relative to the aperture radius, which reduced the effect of reflections from the boundary on the main beam. To reduce the size of the grid required for these calculations, a perfectly matched layer (PML) was recently added to the KZK simulation routines in FOCUS. Simulations of the linear pressure fields generated by a spherically focused transducer with an aperture radius of 1.5 cm and a radius of curvature of 6cm are evaluated for a peak surface pressure of 0.5 MPa and a 1 MHz fundamental frequency. Results of linear KZK simulations with and without the PML are compared to an analytical solution of the linear KZK equation on-axis, and the results show that simulations without the PML require a radial boundary that is at least seven times the aperture radius, whereas the PML enables accurate simulations for a radial boundary that is only two times the aperture radius. [This work was supported in part by NIH Grant R01 EB012079.]
An error reduction algorithm for numeric calculation of the spatial impulse response
Authors: Sponheim Nils
Published: October 2014

The most frequently used method for calculation of the pulsed pressure field of ultrasonic transducers is the spatial impulse response (SIR) method. This paper presents a new numeric approach that reduce the numeric error by weighting the contribution of each source element into the SIR time array, by considering the exact time of arrival of each contribution. The resolution of the time array Δt must be finite. This results in an error in travel time of ±Δt/2. However, we know the exact travel time and based on this, we can share the contribution from each source element between the two closest time elements so that the average time corresponds to the exact travel time and thereby reduce the numeric error. This study compares the old and the new numeric algorithm with the analytic solution for a planar circular disk because it has a simple analytic solution. The paper presents calculations of the SIR for selected points in space and calculations of the RMS-error between the numeric algorithms and the analytic solution. The proposed new numeric algorithm decreases the numeric noise or error with a factor of 5 compared to the old numeric algorithm.
Teaching auscultation visually with low cost system, is it feasible?
Authors: Aguirre Sergio L. , Brum Ricardo , Paul Stephan , Murta Bernardo H. , Jardin Paula P.
Published: October 2014

Cardiac auscultation can generate important information in the diagnosis of diseases. The sounds that the cardiac system provides are understood in the frequency range of human hearing, but in a region of low sensitivity. This project aims to build a low cost didactic software/hardware set for teaching cardiac auscultation technique in Brazilian universities. The frequencies of interest to describe the human cardiac cycle were found in the range of 20 Hz to 1 kHz which includes low frequencies where available low-cost transducers usually have large errors. To create the system, an optimization of the geometry of the chestpiece is being programmed with finite element simulations; meanwhile, digital filters for specific frequencies of interest and an interface based on MATLAB are being developed. There were needed filters for the gallops (20 to 70 Hz), heart beats (20 to 100 Hz), ejection murmurs (100 to 500 Hz), mitral stenosis (30 to 80 Hz), and regurgitations (200 to 900 Hz). The FEM simulation of a chestpiece demonstrates high signaling levels on the desired frequency range, which can be used with the filters to obtain specific information. Furthermore, the ideal signal recording equipments will be defined, implemented, and tested.
Flexural wave induced coherent scattering in arrays of cylindrical shells in water
Authors: Titovich Alexey S. , Norris Andrew N.
Published: October 2014

A periodic array of elastics shells in water is a sonic crystal with local resonances in the form of flexural vibrations. This acoustic metamaterial has seen application in wave steering by grading the index in the array, as well as acoustic filters manifested by Bragg scattering. The primary reason for using shells is that they can be tuned quasi-statically to have water-like effective acoustic properties. The issue is that the modally dense flexural resonances can form pseudogaps in the frequency response resulting in total reflection from the array. Furthermore, if a flexural resonance falls in the Bragg band gap, total transmission is possible at that frequency. Although the scattered wave due to low order flexural vibration of a thin shell is evanescent, when several shells are closely spaced, the effect on the far-field response is dramatic. In this paper, the interaction of neighboring shells is investigated theoretically using the Love-Timoshenko shell theory and multiple scattering. A simple model is offered to describe the interaction of modes based on the analytical work. The directionality of the lowest flexural modes is also discussed as it can lead to phasing between neighboring shells.
A thin-panel underwater acoustic absorber
Authors: Hicks Ashley J. , Haberman Michael R. , Wilson Preston S.
Published: October 2014

We present experimental results on the acoustic behavior of thin-panel underwater sound absorbers composed of a sub-wavelength layered structure. The panels are formed using an inner layer of Delrin or PLA plastic with circular air-filled holes sandwiched between two rubber outer layers. The panel structure mimics a planar encapsulated bubble screen exactly one bubble thick, but displays performance that is significantly more broadband than a comparable bubble screen, which is only useful near the resonance frequency of the bubble. Initial results indicate 10 dB of insertion loss in the frequency range 1 kHz to 5 kHz for a panel that is about 1/250th of a wavelength in thickness at the lowest frequency. The effect of air volume fraction and the use of a 3-D printed (porous) inner layer on insertion loss will be presented and discussed. [Work supported by ONR.]
Micromechanical effective medium modeling of metamaterials of the Willis form
Authors: Muhlestein Michael B. , Haberman Michael R. , Wilson Preston S.
Published: October 2014

The unique behavior of acoustic metamaterials (AMM) results from deeply sub-wavelength structures with hidden degrees of freedom rather than the inherent material properties of their constituents. This distinguishes AMM from classical composite or cellular materials and also complicates attempts to model their overall response. This is especially true when sub-wavelength structures yield anisotropic effective material response, a key feature of AMM devices designed using transformation acoustics. Further, previous work has shown that the dynamic response of heterogeneous materials must include coupling between the overall strain and momentum fields [Milton and Willis, Proc. R. Soc. A 463, 855–880, (2007)]. A micromechanical homogenization model of the overall Willis constitutive equations is presented to address these difficulties. The model yields a low-volume-fraction estimate of anisotropic and frequency-dependent effective properties in the long-wavelength limit. The model employs volume averages of the dyadic Green’s function calculating the particle displacement resulting from a unit force source. This Green’s function is shown to be analogous to one that determines the particle velocity in a fluid resulting from a unit dipole moment. The predicted effective properties for isotropic materials with spherical inclusions fall within the Hashin-Shtrikman bounds and agree with self-consistent estimates. [Work supported by ONR.]
Acoustic metamaterial homogenization based on equivalent fluid media with coupled field response
Authors: Sieck Caleb F. , Haberman Michael R. , Alù Andrea
Published: October 2014

Homogenization schemes for wave propagation in heterogeneous electromagnetic (EM) and elastic materials indicate that EM bianisotropy and elastic momentum-strain and stress-velocity field coupling is required to correctly describe the effective behavior of the medium [Alu, Phys. Rev. B, 84, 075153 (2011); Milton and Willis, Proc. R. Soc. A, 463, 855–880, (2007)]. Further, the determination of material coupling terms in EM resolves apparent violations of causality and passivity which is present in earlier models [A. Alù, Phys. Rev. B, 83, 081102(R) (2011)]. These details have not received much attention in fluid acoustics, but they are important for a proper description of acoustic metamaterial behavior. We derive expressions for effective properties of a heterogeneous fluid medium from expressions for the conservation of mass, the conservation of momentum, and the equation of state and find a physically meaningful effective material response from first-principles. The results show inherent coupling between the ensemble averaged volume strain-momentum and pressure-velocity field. The approach is valid for an infinite periodic lattice of heterogeneities and employs zero-, first-, and second-order tensorial Green’s functions to relate point-discontinuities in compressibility and density to far field pressure and particle velocity fields. [This work was supported by the Office of Naval Research.]
Cloaking of an acoustic sensor using scattering cancelation
Authors: Guild Matthew D. , Alù Andrea , Haberman Michael R.
Published: October 2014

Acoustic scattering cancelation (SC) is an approach enabling the elimination of the scattered field from an object, thereby cloaking it, without restricting the incident wave from interacting with the object. This aspect of an SC cloak lends itself well to applications in which one wishes to extract energy from the incident field with minimal scattering, such as for sensing and noise control. In this work, an acoustic cloak designed based on the scattering cancelation method, and made of two effective fluid layers, is applied to the case of an acoustic sensor consisting of a hollow piezoelectric shell with mechanical absorption, providing a 20–50 dB reduction in the scattering strength. The cloak is shown to increase the range of frequencies over which there is nearly perfect phase fidelity between the acoustic signal and the voltage generated by the sensor, while remaining within the physical bounds of a passive absorber. The feasibility of achieving the necessary fluid layer properties is demonstrated using sonic crystals with the use of readily available acoustic materials. [Work supported by the US ONR and Spanish MINECO.]
Detection and analysis of shock-like waves emitted by heated supersonic jets using shadowgraph flow visualization
Authors: Murray Nathan E.
Published: October 2014

Shock-like waves in the acoustic field adjacent to the shear layer formed by a supersonic, heated jet are observed using the method of retro-reflective shadowgraphy. The two inch diameter jet issued from a converging–diverging nozzle at a pressure ratio of 3.92 with a temperature ratio of 3.3. Image sets were obtained near the jet exit and in the post-potential core region. In both locations, shock-like waves can be observed immediately adjacent to the jet shear layer. Each image is subdivided into a set of overlapping tiles. A radon transform is applied to the auto-correlation of each tile providing a quantitative measure of the dominant propagation direction of waves in each sub-region. The statistical distribution of propagation angles over the image space provides a measure of the distribution of source convection speeds and source locations in the jet shear layer. Results show general agreement with a convection speed on the order of 70 percent of the jet velocity.
Influence of windscreen on impulsive noise measurement
Authors: rasmussen per
Published: October 2014

The nearfield noise from jet engines may contain impulsive sound signals with high crest factors. Most jet engine noise measurements are performed outside in potentially windy conditions, and it may, therefore, be necessary to use windscreens on microphones to reduce the influence of wind induced noise on the microphone. The windscreen will, however, influence the frequency response of the microphone especially at high frequencies. This will change both the magnitude and the phase response and, therefore, change the measured impulse. The effect of different sizes of windscreen is investigated and the effect on impulsive type signals is evaluated both in the time domain and the frequency domain.
Comparison of nonlinear, geometric, and absorptive effects in high-amplitude jet noise propagation
Authors: Reichman Brent O. , Gee Kent L. , Neilsen Tracianne B. , Thaden Joseph J. , James Michael M.
Published: October 2014

In recent years, understanding of nonlinearity in noise from high-performance jet aircraft has increased, with successful modeling of nonlinear propagation in the far field. However, the importance and characteristics of nonlinearity in the near field are still debated. An ensemble-averaged, frequency-domain version of the Burgers equation can be inspected to directly compare the effects of nonlinearity on the sound pressure level with the effects of atmospheric absorption and geometric spreading on a decibel scale. This nonlinear effect is calculated using the quadspectrum of the pressure and the squared pressure waveforms. Results from applying this analysis to F-22A data at various positions in the near field reveal that in the near field the nonlinear effects are of the same order of magnitude as geometric spreading and that both of these effects are significantly greater than absorption in the area of maximum radiation. [Work supported by ONR and an ORISE fellowship through AFRL.]
A study of tongue trajectories for English /æ/ using articulatory signals automatically extracted from lingual ultrasound video
Authors: Mielke Jeff , Carignan Christopher , Dodsworth Robin
Published: October 2014

While ultrasound imaging has made articulatory phonetics more accessible, quantitative analysis of ultrasound data often reduces speech sounds to tongue contours traced from single video frames, disregarding the temporal aspect of speech. We propose a tracing-free method for directly converting entire ultrasound videos to phonetically interpretable articulatory signals using Principal Component Analysis of image data (Hueber et al. 2007). Once a batch of ultrasound images (e.g., 36,000 frames from 10 min at 60 fps) has been reduced to 20 principal components, numerous techniques are available for deriving temporally changing articulatory signals that are both phonetically meaningful and comparable across speakers. Here we apply a regression model to find the linear combination of PCs that is the lingual articulatory analog of the front diagonal of the acoustic vowel space (Z2-Z1). We demonstrate this technique with a study of /æ/ tensing in 20 speakers of North American English varieties with different tensing environments (Labov 2005). Our results show that /m n/ condition a tongue raising gesture that is aligned to the vowel nucleus, while /ɡ/ conditions anticipatory raising toward the velar target. /ŋ/ patterns consistently with the other velar rather than the other nasals.
An acoustic profile of Spanish trill /r/
Authors: Rivera-Campos Ahmed , Boyce Suzanne E.
Published: October 2014

Unlike English rhotic, there is limited data on the acoustic profile of Spanish trill /r/. It is well known that one key aspect of the English rhotic /ɹ/ is the lowering of the F3 formant but limited information can be found if Spanish trill shares the same characteristics. Although it has been described that a lowering of F3 is not something that characterizes /r/ production and that F3 values fall under certain ranges that are delimited by vowel contexts, analysis of F3 values has not been done using a large sample of native speakers of Spanish. The following study analyzed the F3 values of 20 participants after production of /r/ by different native speakers of Spanish from different regions of Latin America, and the Caribbean. Analysis of F3 values of /r/ provides information about articulatory requirements for adequate /r/ production. This information will benefit professionals that service individuals with articulatory difficulties or are learning Spanish as a second language.
Investigation of the role of the tongue root in Kazakh vowel production using ultrasound
Authors: Washington Jonathan N.
Published: October 2014

It has been argued that Kazakh primarily distinguishes its anterior ("front") vowels from its posterior ("back") vowels through retraction of the tongue root. This analysis is at odds with the traditional assumption that the anteriority of Kazakh vowels is contrasted by tongue body position. The present study uses ultrasound imaging to investigate the extent to which the position of the tongue root and the tongue body are involved in the anteriority contrast in Kazakh. Native speakers of Kazakh were recorded reading words (in carrier sentences) containing target vowels, which were controlled for adjacent consonants and metrical position. An audio recording was also made of these sessions. Frames containing productions of the target vowels were extracted from the ultrasound video and the imaged surface of the tongue was manually traced. Analyses of tongue root and body position were analyzed for each vowel and will be presented together with formant measurements from the audio recordings.
Vowel production in sighted children and congenitally blind children
Authors: Menard Lucie , Turgeon Christine
Published: October 2014

It is well known that vision plays an important role in speech perception. At the production level, we have recently shown that speakers with congenital visual deprivation produce smaller displacements of the lips (visible articulator) compared to their sighted peers [L. Ménard, C. Toupin, S. Baum, S. Drouin, J. Aubin, and M. Tiede, J. Acoust. Soc. Am. 134, 2975–2987 (2013)]. To further investigate the impact of visual experience on the articulatory gestures used to produce intelligible speech, a speech production study was conducted with blind and sighted school-aged children. Eight congenitally blind children (mean age: 7 years old, from 5 years to 11 years) and eight sighted children (mean age: 7 years old, from 5 years to 11 years) were recorded using a synchronous ultrasound and Optotrak imaging system to record tongue and lip positions. Repetitions of the French vowels /i/, /a/, and /u/ were elicited in a /bVb/ sequence in two prosodic conditions: neutraland under contrastive focus. Tongue contours, lip positions, and formant values were extracted. Acoustic data show that focused syllables are less differentiated from their unfocused counterparts in blind children than in sighted children. Trade-offs between lip and tongue positions are examined.
Spectral and duration cues of English vowel identification for Chinese-native listeners
Authors: Tao Sha , Mi Lin , Wang Wenjing , Dong Qi , Liu Chang
Published: October 2014

This study was to investigate how Chinese-native listeners use spectral and duration cues for English vowel identification. The first experiment was to examine whether Chinese-native listeners’ English vowel perception was related to their sensitivity to the change of vowel formant frequency that is a critical spectral cue to vowel identification. Identification of 12 isolated American English vowels was measured for 52 Chinese college students in Beijing. Thresholds of vowel formant discrimination were also examined for these students. Results showed that there was a significantly moderate correlation between Chinese college students’ English vowel identification and their thresholds of vowel formant discrimination. That is, the lower vowel formant threshold of listeners, the better vowel identification. However, the moderate correlation between vowel identification and formant discrimination suggested some other factors accounting for the individual variability in English vowel identification for Chinese-native listeners. In Experiment 2, vowel identification was measured with and without duration cues, showing that vowel identification was reduced by 5.1% when duration cue was removed. Further analysis suggested that for the listeners who depended less on duration cue, the better thresholds of formant discrimination, the higher scores of vowel identification, but no such correlation for listeners who used duration cues remarkably.
Effect of phonetic training on the perception of English consonants by Greek speakers in quiet and noise conditions
Authors: Lengeris Angelos , Nicolaidis Katerina
Published: October 2014

The present study employed high-variability phonetic training (multiple words spoken by multiple talkers) to improve the identification of English consonants by native speakers of Greek. The trainees completed five sessions of identification training with feedback for seven English consonants (contrasting voiced vs. voiceless stops and alveolar vs. postalveolar fricatives) each consisting of 198 trials with a different English speaker in each session. Another group of Greek speakers served as controls, i.e., completed the pre/post test but received no training. Pre/post tests included English consonant identification in quiet and noise. In the noise condition, participants identified consonants in the presence of a competing English speaker at a signal-to-noise ratio of -2dB. The results showed that training significantly improved English consonant perception for the group that received training but not for the control group in both quiet and noise. The results add to the existing evidence that supports the effectiveness of the high-variability approach to second-language segmental training.
Perceptual warping of phonetic space applies beyond known phonetic categories: Evidence from the perceptual magnet effect
Authors: Pajak Bozena , Piccinini Page , Levy Roger
Published: October 2014

What is the mental representation of phonetic space? Perceptual reorganization in infancy yields a reconfigured space “warped” around native-language (L1) categories. Is this reconfiguration entirely specific to L1 category inventory? Or does it apply to a broader range of category distinctions that are non-native, yet discriminable due to being defined by phonetic dimensions informative in the listener’s L1 (Bohn & Best, 2012; Pajak, 2012)? Here we address this question by studying perceptual magnets, which involve attrition of within-category distinctions and enhancement of distinctions across category boundaries (Kuhl, 1991). We focus on segmental length, known to yield L1-specific perceptual magnets: e.g., L1-Finnish listeners have one for [t]/[tt], but L1-Dutch listeners, who lack (exclusively) length-based contrasts, do not (Herren & Schouten, 2008). We tested 31 L1-Korean listeners in an AX discrimination task for [n]-[nn] and [f]-[ff] continua. Korean listeners have been shown to discriminate both (Pajak, 2012), despite only having the former set in the inventory. We found perceptual magnets for both continua, demonstrating that perceptual warping goes beyond the specific L1 categories: when a phonetic dimension is informative for contrasting some L1 categories, perceptual warping applies not only to the tokens from those categories, but also to that dimension more generally.
Processing of English-accented Spanish voice onset time by Spanish speakers with low English experience
Authors: Llanos Fernando , Francis Alexander L.
Published: October 2014

Previous research (Llanos & Francis, 2014) shows that the processing of foreign accented speech sounds can be affected by listeners’ familiarity with the language that causes the accent. Highly familiar listeners treat foreign accented sounds as foreign sounds while less familiar listeners treat them natively. The present study tests the hypothesis that less familiar listeners may nevertheless be able to apply foreign categorization patterns to accented words by recalibrating phonetic expectations according to acoustic information provided by immediate phonetic context. Two groups of Spanish native speakers with little English experience will identify tokens drawn from a digitally edited VOT continuum ranging from baso "glass" (-60 ms VOT) to paso "step" (60 ms VOT). Tokens are embedded in a series of Spanish words beginning with /b/ and /p/ to provide phonetic context. In the English-accented condition, context words are digitally modified to exhibit English-like VOT values for /b/ (10 ms) and /p/ (60 ms). In the Spanish condition, these tokens are edited to exhibit prototypical Spanish /b/ (-90 ms) and /p/ (10 ms) VOT values. If listeners can accommodate foreign accented sounds according to expectations provided by immediate phonetic context, then listeners’ VOT boundary in the English-accented condition should be significantly higher than in the Spanish condition.
Stimulus length and scale label effects on the acoustic correlates of foreign accent ratings
Authors: McCullough Elizabeth A.
Published: October 2014

Previous studies have investigated acoustic correlates of accentedness ratings, but methodological differences make it difficult to compare their results directly. The present experiment investigated how choices about stimulus length and rating scale labels influence the acoustic correlates of listeners’ rating responses. Four conditions crossed two stimulus lengths (CV syllable vs. disyllabic word) with two sets of rating labels (“no foreign accent”/“strong foreign accent” vs. “native”/“not native”). Monolingual American English listeners heard samples of English from native speakers of American English, Hindi, Korean, Mandarin, and Spanish and indicated their responses on a continuous rating line. Regression models evaluated the correlations between listeners’ ratings and a variety of acoustic properties. Patterns for accentedness and non-nativeness ratings were identical. VOT, F1, and F2 correlated with ratings on all stimuli, but vowel duration correlated with ratings on disyllabic word stimuli only. If vowel duration is interpreted as a reflection of global temporal properties, this result suggests that listeners may perceive such properties in utterances as short as two syllables. Thus, stimulus design is vital in identifying components of foreign accent perception that are related to differences between a talker’s first and second languages as opposed to components that are related to general fluency.
When two become one—Orthography helps link two free variants to one lexical entry
Authors: Yang Chung-Lin , Darcy Isabelle
Published: October 2014

L2 learners can become better at distinguishing an unfamiliar contrast by knowing the corresponding orthographic forms (e.g., Escudero et al., 2008). We ask whether learners could associate two free variants with the same lexical entry when the orthographic form was provided during learning. American learners learned an artificial language where [p]-[b] were in free variation (both were spelled as
) (test condition) while [t]-[d] were contrastive (control condition), or vice-versa ([t]-[d] in test, counterbalanced across subjects). Using a word-learning paradigm modified from Hayes-Harb et al. (2010), in the learning phase, participants heard novel words paired with pictures. One subgroup of learners saw the spellings as well (“Orth+”), while another did not (i.e., auditory only, “Orth−”). Then in a picture-auditory word matching task, the new form of the word was paired with the original picture. Orth + learners were expected to be more accurate at accepting the variant as the correct label for the original test item than Orth−. The results showed that Orth + learners detected and learned the [p]-[b] free variation significantly better than Orth− (p < 0.05), but not the [t]-[d] free variation. Thus, the benefit of orthography in speech learning could vary depending on the specific contrasts at hand.
Elastic features visible on canonical targets with high frequency imaging during the 2014 St. Andrews Bay experiments
Authors: Marston Philip L. , Marston Timothy M. , Kargl Steven G. , Plotnick Daniel S. , Espana Aubrey , Williams Kevin L.
Published: October 2014

During the 2014 St. Andrews Bay experiments some canonical metallic targets (a hollow sphere and some circular cylinders) were viewed with a synthetic aperture sonar (SAS) capable of acquiring data using a 110–190 kHz chirped source. The targets rested on mud-covered sand and were typically at a range of 20 m. Fast reversible SAS processing using an extension of line-scan quasi-holography [K. Baik, C. Dudley, and P. L. Marston, J. Acoust. Soc. Am. 130, 3838–3851 (2011)] was used to extract relevant signal content from images. The significance of target elastic responses in extracted signals was evident from the frequency response and/or the time-domain response. For example, the negative group velocity guided wave enhancement of the backscattering by the sphere was clearly visible near 180 kHz. [For a ray model of this type of enhancement see: G. Kaduchak, D. H. Hughes, and P. L. Marston, J. Acoust. Soc. Am. 96, 3704–3714 (1994).] In another example, the timing of a sequence of near broadside echoes from a solid aluminum cylinder was consistent with reflection and internal reverberation of elastic waves. These observations support the value of combining reversible imaging with models interpreted using rays. [Work supported by ONR and SERDP.]
Denoising structural echoes of elastic targets using spatial time–frequency distributions
Authors: Sabra Karim G.
Published: October 2014

Structural echoes of underwater elastic targets, used for detection and classification purposes, can be highly localized in the time–frequency domain and can be aspect-dependent. Hence, such structural echoes recorded along a distributed (synthetic) aperture, e.g., using a moving receiver platform, would not meet the stationarity and multiple snapshots requirements of common subspace array processing methods used for denoising array data based on their estimated covariance matrix. To handle these scenarios, a generalized space–time–frequency covariance matrix can be computed from the single-snapshot data using Cohen’s class time-frequency distributions between all sensor data pairs. This space–time–frequency covariance matrix automatically accounts for the inherent coherence across the time-frequency plane of the received nonstationary echoes emanating from the same target. Hence, identifying the signal’s subspace from the eigenstructure of this space–time–frequency covariance matrix provides a means for denoising these non-stationary structural echoes by spreading the clutter and noise power in the time–frequency domain. The performance of the proposed methodology will be demonstrated using numerical simulations and at-sea data.
Predicting the acoustic response of complicated targets in complicated environments using a hybrid finite element/propagation model
Authors: Espana Aubrey L. , Williams Kevin L. , Kargl Steven G. , Nijhof Marten J. , Plotnick Daniel S. , Marston Philip L.
Published: October 2014

Previous work has shown that hybrid finite element (FE)/propagation models are a viable tool for estimating the Target-In-The-Environment-Response, or TIER, for simple shapes such as cylinders and pipes on a flat, undisturbed sand/water interface [K. L. Williams et al., J. Acoust. Soc. Am 127, 3356–3371 (2010)]. Here we examine their use for more complicated targets located in complicated ocean environments. The targets examined include various munitions and ordnance-like targets, with intricate internal structure and filled with either air or water. A hybrid FE/propagation model is used to predict their TIER on flat, undisturbed sand. Data acquired during the target portion of TREX13 is used to validate the model results. Next, the target response is investigated in a more complicated environment, being partially buried with their axis tilted w.r.t. the flat sand interface. Again model results are validated using TREX13 data, as well as data acquired in a controlled tank experiment. These comparisons highlight the feasibility of using hybrid models for complex target/environment configurations, as well possible limitations due to the effects of multiple scattering.
Detection and classification of marine targets buried in the sediment using structural acoustic features
Authors: Bucaro Joseph , Houston Brian , Sarkissian Angie , Simpson Harry , Waters Zack , Yoder Timothy , Amon Dan
Published: October 2014

We present research on detection and classification of underwater targets buried in a saturated sediment using structural acoustic features. These efforts involve simulations using NRL’s STARS3D structural acoustics code and measurements in the NRL free-field and sediment pool facilities, off the coast of Duck, NC, and off the Coast of Panama City, FL. The measurements in the sediment pool demonstrated RVM classifiers trained using numerical data on two features—target strength correlation and elastic highlight image symmetry. Measurements off the coast of Duck were inconclusive owing to tropical storms resulting in a damaged projector. Extensive measurements were then carried out in 60 ft. of water in the Gulf using BOSS, an autonomous underwater vehicle with 40 receivers on its wings. The target field consisted of nine simulant-filled UXO and two false targets buried in the sediment and twenty proud targets. The AUV collected scattering data during north/south, east/west, and diagonal flights. We discuss the data analyzed so far from which we have extracted 3-D images and acoustic color constructs for 18 of the targets and demonstrated UXO/false target separation using a high dimensional acoustic color feature. Finally, we present related work involving targets buried in non-saturated elastic sediments. [This work is supported by ONR and SERDP.]
Performance metrics for depth-based signal separation using deep vertical line arrays
Authors: Boyle John K. , Kniffin Gabriel P. , Zurk Lisa M.
Published: October 2014

A publication [McCargar & Zurk, 2013] presented a method for passive depth-separation of signals received on vertical line arrays (VLAs) deployed below the critical depth in the deep ocean. This method, based on a modified Fourier transform of the received signals from submerged targets, makes use of the depth-dependent modulation inherent in the signals due to interference between the direct and surface-reflected acoustic arrivals. Examination of the transform is necessary to determine performance of the algorithm in terms of the minimum target depth and range, array aperture, and temporal sampling. However, traditional expressions for signal sampling requirements (Nyquist sampling theorem) do not directly apply to the measured signal along a target trace due to uneven sampling in vertical angle imposed by the spatiotemporal evolution of the target track as observed on the VLA. In this paper, the effects of this uneven sampling on the ambiguity in the estimated depth (i.e., aliasing) are discussed, and expressions for the maximum snapshot length are presented and validated using simulated data produced with a normal-mode propagation model. Initial results are presented to show the requirements for snapshot lengths and target trajectories for successful depth separation of slow moving targets at low frequencies.
Sound reinforcement in an acoustically challenging multipurpose space
Authors: Britton Deb
Published: October 2014

Often times, sound system designers are dealt less than ideal cards: design a sound reinforcement system that will provide great speech intelligibility, in a highly reverberant space, without modifying any of the architectural finishes. While this can certainly be a challenge, add to those prerequisites, the additional complication of the sound system serving a multi-purpose use, where different types of presentations must take place in different locations in the space, and with varying audience sizes. This paper presents a case study of such a scenario, and describes the approach taken in order to achieve the client’s goals.
Enhancements in technology for improving access to active acoustic solutions in multipurpose venues
Authors: Freiheit Ronald
Published: October 2014

With advancements in digital signal processing technology and higher integration of functionality, access to active acoustics systems for multipurpose venues has been enhanced. One of the challenges with active acoustics systems in multipurpose venues is having enough control over the various acoustic environments within the same room (e.g., under balcony versus over balcony). Each area may require its own signal processing and control to be effective. Increasing the signal processing capacity to address these different environments will provide a more effective integration of the system in the room. A new signal processing platform with the flexibility to meet these needs is discussed. The new platform addresses multiple areas with concurrent processing and is integrated with a digital audio buss and a network-based control system. The system is flexible in its ability to easily expand to meet the needs of a variety of environments. Enhancing integration and flexibility of scale accelerates the potential for active systems with an attractive financial point of entry.
Development of a tunable absorber/diffuser using micro-perforated panels
Authors: Hildebrand Matthew S.
Published: October 2014

Shared rehearsal spaces are an all-too-common compromise in music education, pitting vocal, and instrumental ensembles against each other for desirable room acoustics. More than ever, adjustable acoustics are needed in music spaces. An innovative new acoustic panel system was developed with this need for flexibility in mind. Providing variable sound absorption with a truly static aesthetic, control of reverberation time in the mid-frequency bands is ultimately handed over to the end user. New product development test methods and critical design decisions are discussed, such as curving the micro-perforated panel to improve scattering properties. In situ reverberation measurements are also offered against a 3D CAD model prediction using lab-tested material properties.
Real case measurements of inflatable membranes absorption technique
Authors: Adelman-Larsen Niels W.
Published: October 2014

After some years of development of the patented technology of inflated plastic membranes for sound absorption, an actual product became available in 2012 and immediately implemented in a Danish music school. It absorbs sound somewhat linearly from 63 to 1k Hz, when active, advantageous for amplified music. The absorption coefficient is close to 0.0 when deactivated. 75.000 ft2 of the mobile version of the innovation was employed at the Eurovision Song Contest, the second largest annual television event worldwide. This contributed to a lowering of T30 in the 63, 125, and 250 Hz octave bands from up to 13 s to below 4 s in the former-shipyard venue. The permanently installed version has been incorporated in a new theater in Korea. More detailed acoustic measurements from these cases will be presented. The technology will further be used in the new, multi-functional Dubai Opera scheduled for 2015.
Virtual sound images and virtual sound absorbers misinterpreted as supernatural objects
Authors: Waller Steven J.
Published: October 2014

Complex sound behaviors such as echoes, reverberation, and interference patterns can be mathematically modeled using the modern concepts of virtual sound sources or virtual sound absorbers. Yet prior to the scientific wave theory of sound, these same acoustical phenomena were considered baffling, and hence led to the illusion that they were due to mysterious invisible sources. Vivid descriptions of the physical forms of echo spirits, hoofed thunder gods, and pipers’ stones, as engendered from the sounds they either produced or blocked, are found in ancient myths and legends from around the world. Additional pieces of evidence attesting to these beliefs are found in archaeological remains consisting of canyon petroglyphs, cave paintings, and megalithic stone circles. Blindfolded participants in acoustic experimental set-ups demonstrated that they attributed various virtual sound effects to real sound sources and/or attenuators. Ways in which these types of sonic phenomena can be manipulated to give rise to ultra-realistic auditory illusions of actual objects even today will be discussed relative to enhancing experiences of multimedia entertainment and virtual reality. Conversely, understanding how the mind can construct psychoacoustic models inconsistent with scientific reality could serve as a lesson helping prevent the supernatural misperceptions to which our ancestors were susceptible.