bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact wave attenuation using Maxwell-type oscillators in dissipative elastic metamaterials
Authors: Alamri Sagr , Li Bing , Tan Kwek Tze
Published: April 2018

This work studies the development of a dissipative elastic metamaterial with single and dual-Maxwell type resonator for stress wave mitigation. Mass-spring-damper elements are used to model and analyze the mechanism of wave dissipation effect on the vibration characteristics. It is found that broadband wave attenuation region can be obtained and expanded to a wider range by properly utilizing interactions from resonant motions and viscoelastic effects of the Maxwell-type oscillators. In addition, numerical verifications are conducted for various cases, and excellent agreement between theoretical and numerical frequency response functions are obtained. The design of this dissipative metamaterial system is further applied for blast wave mitigation. By means of the bandgap merging effect that is induced by the Maxwell-type oscillator, the passing blast wave can be almost completely suppressed in the low-frequency range. A significantly improved performance of the proposed dissipative metamaterials for stress wave mitigation is verified in both time and frequency domains.
The impact of perceptual load on natural and synthetic speech perception
Authors: Ojeda Adriana , Kutlu Ethan , Wayland Ratree
Published: April 2018

Previous work has shown that the availability and the weighting of different types of information (e.g., lexical, segmental/subsegmental, and metrical prosody) for speech segmentation are gradiently affected by perceptual and cognitive load. Specifically, it has been shown that severe energetic masking increases reliance on the acoustic, sub-segmental, context-dependent coarticulation information and decreases reliance on lexical information (e.g., Mattys et al., 2009). In this study, the effects of energetic masking on the intelligibility of synthetic and natural speech (controlled for lexical and metrical prosody) will be compared. Since fine acoustic detail linked to coarticulation is lacking in synthetic speech in comparison to naturally produced speech, energetic masking should result in greater reliance on lexical information than coarticulatory information on synthetic speech processing while the opposite will be true for natural speech. Reference Mattys, S. L., Brooks, J., & Cooke, M. (2009). Recognizing speech under a processing load: Dissociating energetic from informational factors. Cognitive Psychology, 59, 203-243.
Asymmetries in vowel perception arise from phonetic encoding strategies
Authors: Masapollo Matthew , Franklin Lauren , Morgan James , Polka Linda
Published: April 2018

Directional asymmetries in vowel discrimination studies reveal that speech perceivers (both adult and infant) are biased toward extreme vocalic articulations, which lead to acoustic vowel signals with well-defined spectral prominences due to formant convergence. These directional effects occur with vowel stimuli presented in either the acoustic or the visual modality and are independent of specific linguistic experience. Current research is focused on elucidating the perceptual processes underlying this universal vowel bias. In the present investigation, the inter-stimulus interval (ISI) in AX discrimination tasks for unimodal acoustic and visual vowels was manipulated (500 ms vs. 1000 ms) in order to examine whether asymmetries are present under experimental conditions that reduce demands on attention and working memory. Subjects discriminated either video-only or audio-only tokens of naturally-spoken English [u] and French [u] which differ in their degree of visible lip-rounding and proximity between F1 and F2. We observed robust asymmetries with these stimuli with English- and French-speaking adults in earlier studies using a relatively long ISI (1500 ms). The present results demonstrated that asymmetries in both auditory and visual vowel discrimination are diminished in the short ISI conditions, suggesting that this vowel bias derives from phonetic encoding processes, rather than general psychophysical processes.
Sinewave vowel sounds: The role of vowel qualities, frequencies and harmonicity of sinusoids, and perceived pitch for vowel recognition
Authors: Maurer Dieter , Suter Heidy , Kathiresan Thayabaran , Dellwo Volker
Published: April 2018

In the literature, the recognition of sinewave vowels replicating statistical formant patterns is reported as impaired when compared to natural sounds. However, the corresponding formant simulating sinusoids were harmonically unrelated, with synthesised signals only accidentally being quasi-periodic, and vowel confusion was indicated to relate to vowel height. Involving five phonetic expert listeners, the present study tested vowel and pitch recognition of three sinusoid replicas based on statistical F1-F2-F3 patterns of the Standard German closed and mid-open vowels /i-y-e-ø-o-u/ for women, “corrected” approximations of these patterns with harmonically related sinusoids, and harmonical patterns with fixed first and third sinusoids, yet varying only the second sinusoid so as to effect a change in harmonic relation. The results showed strong vowel confusions for mid-open but only limited confusions for closed vowels. Additional effects on vowel recognition were indicated to concern harmonicity and specific frequencies of the sinusoids, and perceived pitch (range recognised = 165-440Hz). Thus, sinewave replications of formant frequencies seem to represent perceived vowel qualities not per se but only in relation to specific vowel qualities, sinusoid configuration and pitch, supporting earlier claims of spectral representation of vowel quality as being non-systematic and pitch-related.
Listeners compensate for prosodic position when categorizing word-final obstruents
Authors: Steffman Jeremy
Published: April 2018

This study explores how perceptual sensitivities to contextual variability extend to prosodically induced variation. In English, vowel duration is reliably longer preceding a voiced obstruent, as opposed to a voiceless obstruent, and listeners use preceding length as a cue to obstruent voicing (e.g. Raphael, 1972). Segmental duration also co-varies systematically with prosodic position, being longer phrase-finally (e.g. Turk & Shattuck-Hufnagel, 2007). In this study, we tested the extent to which listeners’ categorization of word-final obstruents is altered by the prosodic position of the target. Participants heard a continuum that varied only in vowel length, and categorized stimuli as either “coat” or “code”. Prosodic position in a carrier phrase was manipulated by splicing the target word into either a phrase-final or phrase-medial context. Results show listener expectations about phrase final lengthening mediate categorization, with significantly longer vowel durations required in phrase-final position for a “code” response. The results are discussed in terms of other top-down influences on segmental categorization (e.g. lexical information), and implications for further work on the prosody-phonetics interface.
A replication of competition and prosodic effects on spoken word recognition
Authors: Warner Natasha L. , Hernandez Genesis G. , Park Seongjin , McQueen James M.
Published: April 2018

Despite the absence of clear and reliable word boundary markers, listeners recognize words in spoken sentences. A previous study tested a spoken-word recognition model, Shortlist, by asking speakers of British English to identify real words within nonwords (McQueen, Norris & Cutler, 1994). Some words were embedded within the onsets of longer words with either a weak-strong (WS) or strong-weak (SW) stress pattern (e.g., “mess” in /dəmɛs/, the onset of “domestic,” “sack” in /sækɹɪf/, the onset of “sacrifice"), and other words were embedded without a real word onset with either a WS or SW pattern (e.g., /nəmɛs/ or /mɛstəm/ for “mess” and /sækɹək/ or /kləsæk/ for “sack”). The original study reported both competition effects (e.g. competition from “domestic” hindered recognition of “mess") and prosodic effects (e.g. the stress in “mess” facilitated segmenting it from the preceding context). This current study aimed to replicate these results in American-English. Despite the different listener population and dialect, pilot results for the current study confirm both types of effect. This data will be used to test a new American English version of the Shortlist-B model of spoken word recognition (Norris & McQueen, 2008).
The time course of word recognition in younger and older adults: Signal degradation and lexical challenge
Authors: Van Engen Kristin , Dey Avanti , Runge Nichole , Sommers Mitchell , Spehar Brent , Peelle Jonathan E.
Published: April 2018

As listeners age, speech recognition often becomes more challenging, especially in noisy environments. Older adults also appear to have more difficulty resolving lexical competition than do younger adults. Relatively little is known, however, about how such signal- and lexicon-related challenges interact to affect the timing of word recognition and how such effects might change across the lifespan. In this study, we use a visual world paradigm to investigate the effects noise, word frequency, and phonological neighborhood density on the time course of spoken word recognition in young and older adults. On each trial, listeners saw four items on a computer screen and heard “Click on the” followed by a target word that corresponded to one of the images. None of the other items on the display were phonologically or semantically related to the target. Eye-tracking results show that the time course of word recognition is predicted by age, noise, frequency, density, and several of their interactions. In general, high-frequency words and words from dense phonological neighborhoods were fixated more quickly, while noise and age slowed recognition. These results support a framework in which lexical and acoustic factors co-determine the cognitive challenges associated with speech perception.
Across-ear integration of acoustic-phonetic information under competitive conditions: Effects of attenuation increase in the presence of an extraneous formant
Authors: Summers Robert J. , Roberts Brian
Published: April 2018

Previous research using consonant-vowel syllables where one ear receives the first formant (F1) and the other receives the second and third has shown that dichotic release from masking allows F2 + F3 to remain effective speech cues even after substantial attenuation. This study used three-formant analogues of natural sentences and extended the approach to include competitive conditions. Target formants were presented dichotically (F1 + F3; F2), either alone or accompanied by an extraneous competitor for F2 (i.e., F1±F2C + F3; F2) that listeners must reject to optimize recognition. In experiment 1, F2C was absent and F2 was attenuated in 6-dB steps (range: -6-48 dB). Intelligibility was unaffected until attenuation >30 dB; F2 still provided useful information at 48-dB attenuation. In experiment 2, F2 was attenuated in 12-dB steps (range: 0-36 dB). F2C was created by inverting the F2 frequency contour and using the F2 amplitude contour without attenuation. When F2C was present, 12-dB attenuation was sufficient to cause some loss of intelligibility; the effect was large when attenuation ≥24 dB. This interaction suggests that some mandatory across-ear spectral integration occurs, such that informational masking arising from F2C rapidly swamps the acoustic-phonetic information carried by F2 as its relative level is attenuated. [Work supported by ESRC.]
Multimodal perception of interrupted speech and text by younger and older adults
Authors: Miller Rachel E. , Fogerty Daniel
Published: April 2018

The current study aimed to identify how partial auditory (speech) and visual (text) information are resolved for sentence recognition by younger and older adults. Interrupted speech was created by periodically replacing speech with silent intervals at various interruption rates. Likewise, interrupted text was created by periodically replacing printed text with white space. Speech was further processed by low-pass filtering the stimulus spectrum at 2000 Hz. Speech and text stimuli were interrupted at 0.5, 2, 8, and 32 Hz and presented in unimodal and multimodal conditions. Overall, older listeners demonstrated similar performance to younger listeners on the unimodal conditions. However, there was a marked decrease in performance by older listeners during multimodal testing, suggesting increased difficulty in integrating information across modalities. Performance for both groups improved with higher interruption rates for both text and speech in unimodal and multimodal conditions. Listeners were also able to gain benefit from most multimodal presentations, even when the rate of interruption was mismatched between modalities. Supplementing speech with incomplete visual cues can improve sentence intelligibility and compensate for degraded speech in adverse listening conditions. However, the magnitude of multimodal benefit appears mitigated by age-related changes in integrating information across modalities. [Work supported, in part, by NIH/NIDCD.]
Is the target of imitation directly acoustic or a pattern within a speaker’s phonetic system?
Authors: Scarborough Rebecca , Nielsen Kuniko
Published: April 2018

Speakers may converge phonetically with another talker to whose speech they are exposed, resulting in reduced acoustic distance between interlocutors. However, it is unclear whether the target of imitation is raw acoustics or a linguistic pattern. Zellou et al. (2016) present a case that distinguishes these possibilities: after listening to a model talker whose speech was manipulated to reduce coarticulatory vowel nasality (measured acoustically in A1-P0), participants’ nasality also decreased in post-test productions, relative to their baseline. However, the model speaker had naturally low A1-P0 (correlated with high nasality), and even after the manipulation to raise A1-P0, it was lower than all participants’. If the target of imitation is acoustic, participants diverged from the model (raised A1-P0). But if the target of imitation is a linguistic pattern (decreased coarticulatory nasality), participants converged. The current study uses an AXB perceptual task to determine whether it is acoustically more similar items (more nasal; speakers’ baseline) or linguistically more similar items (less nasal; post-test) that listeners judge as “more similar” to the model talker’s production. A generalized linear mixed model showed a significant preference for post-test items (55.4%, z = 5.19), indicating that linguistic similarity is the basis for listeners’ similarity judgments.
The effects of lexical and phonological factors on talker processing
Authors: Abu El Adas Sandy , Levi Susannah V.
Published: April 2018

Previous research has shown that listeners are better at processing talker information in their native language compared to an unfamiliar language, a phenomenon known as the Language Familiarity Effect. Several studies have explored the cause of this effect. Some have argued that it is tied to the lexicon and the ability to comprehend, while others have suggested that it is the familiarity with the phonology. In the current study, we use an AX discrimination task to test these two factors simultaneously by manipulating lexical status (words/nonwords) and phonotactic probability (high/low). We also test individual differences in reading ability, as poor phonological awareness skills are linked to reading impairment. Twenty-four native speakers of American English completed the AX task and a battery of phonological awareness tasks. Reaction time results revealed an interaction between lexical status and phonotactic probability: words with high phonotactic probability were processed faster than words with low phonotactic probability, but no difference was found for the nonwords. Sensitivity (A’) revealed no effects of lexical status or phonotactic probability, but did reveal that listeners with higher reading scores were more sensitive to talker differences.
Perceptual similarity judgments of voices: Effects of talker and listener language, vocal source acoustics, and time-reversal
Authors: Furbeck Kristina , Thurston Emily J. , Tin Jessica , Perrachione Tyler K.
Published: April 2018

Listeners demonstrate reliable perceptual biases favoring voices speaking their native language versus those speaking a foreign language. This “language-familiarity effect” for voice processing has been found even for perceptual similarity judgments: Voices speaking listeners’ native language sound less alike, even when those recordings have been rendered incomprehensible via time-reversal. Here, we sought to replicate and extend this finding of linguistic effects on voice similarity. Native English- and Mandarin-speaking listeners (both N = 40) rated the perceptual similarity of voices speaking English or Mandarin (both N = 20) for either time-reversed or forward speech. Both listener groups tended to find Mandarin-speaking voices more dissimilar, but this effect was reduced for English-speaking listeners, especially for forward speech. Perceptual similarity judgments of voices were always highly correlated between listener groups and between forward/time-reversed speech. Acoustic measurements (voice fundamental frequency mean and variance, local jitter, harmonics-to-noise ratio, speech rate, and formant dispersion) were also made to ascertain how listeners’ perceptual similarity judgments were related to speech acoustics and whether these relationships differed under time-reversal or across listeners’ or talkers’ native language. Overall, these data suggest that, while native language may influence perceptual dissimilarity of voices, the magnitude of these effects tend to be very small.
Re-examining the effect of top down processing on voice perception
Authors: Quinto Ashley , Kim Kylee , Levi Susannah V.
Published: April 2018

The current study aimed to replicate a recent study conducted by Narayan, Mak, & Bialystok (2016) that found effects of top-down linguistic information on a talker discrimination task by comparing four conditions: compounds (day-dream), rhymes (day-bay), reverse compounds (dream-day), and unrelated words (day-bee). The original study used both within- and across-gender pairs and same and different trials were analyzed separately, obscuring possible response biases. Narayan et al. found graded performance between the four conditions, but some results were likely to have been influenced by the use of across-gender trials in the different-talker condition. In the current study, only female speakers were used and results were analyzed with signal detection theory (sensitivity and bias measures). Results revealed that participants were faster to respond to rhyming pairs than the three other conditions. In addition, participants were significantly more sensitive to talker differences in rhyming pairs than unrelated pairs, but no other conditions differed. Participants were more biased to respond “same” in the rhyme and compound conditions than in the unrelated condition. These results demonstrate a partial replication of the Narayan, Mak, & Bialystok (2016) findings, suggesting an interaction between linguistic and talker information during speech perception.
Perception of femininity in normally phonated and whispered speech
Authors: Houle Nichole , Levi Susannah V.
Published: April 2018

Many transgender women seek out voice and communication therapy to support in their transition from their biological gender to presenting as their gender identity. This has led to an increased need to examine the perception of gender and femininity to develop evidence-based therapy practices. In this study, we explored perception of femininity in normally phonated and whispered speech. Transgender male-to-female, cismale, and cisfemale speakers were recorded producing hVd words. Naïve listeners rated femininity using a visual-analog scale. The results revealed that listeners rated speakers more ambiguously in whispered speech than normally phonated speech. Within-group analyses were conducted to further examine how speaker characteristics (height, age, mean f0, duration) contributed to perceptions of femininity. While there was a significant effect of mean f0 within the normally phonated condition for all groups, none of the other speaker or acoustic cues consistently predicted listener ratings of femininity across speaker groups.
Investigating the influence of listener attitudes and expectations on the intelligibility of Hindi-influenced English
Authors: Vasandani Veera S. , Babel Molly E. , Munson Benjamin
Published: April 2018

Phoneme recognition and speech intelligibility can be affected by purely social factors, such as beliefs about or attitudes toward speakers of varying races and ethnicities (e.g., Babel & Russell, J. Acoust. Soc. Am. 137 [2015]). The current study examined whether implicit and explicit attitudes about people from South Asian (SA) affect the intelligibility of Hindi-influenced English (HIE). Three measures were used: an Implicit Association Test (IAT) to measure general associative attitudes toward SA individuals; an intelligibility task in which listeners repeated HIE and North American English (NAE) sentences in noise, accompanied by pictures of SA or white individuals; and an ethnographic interview to acquire qualitative data about stereotypes, communicative practices with nonnative speakers, and other language attitudes. Data collection is ongoing in a more ethnically diverse location (Vancouver, BC) and a more homogenous one (Minneapolis, MN). Drawing from past studies on socioindexical influences on nonnative speech, we predict that individuals who harbor negative attitudes and stereotypes about SA people will perceive HIE as less intelligible than those without such beliefs. The results of this study will inform the growing body of literature regarding the ways in which socioindexical factors influence speech recognition across individuals with diverse ethnicities and language varieties.
The perception of sexual orientation through speech: Generational change
Authors: Obeda Lily , Munson Benjamin
Published: April 2018

Previous research has shown that listeners can perceive the sexual orientation of some lesbian, gay, and bisexual (LGB) people at a greater than chance levels based on the acoustic-perceptual characteristics of their speech (Munson et al., J. Phonetics [2006], Pierrehumbert et al., J. Acoust. Soc. Am. [2004]). The cues to these judgments were the pronunciation of specific sounds (i.e., /æ/, /ɛ/, /oʊ/, /u/, /s/), rather than global speech characteristics (like f0 range or formant-frequency scaling). In the years since those studies were conducted, societal attitudes toward LGB people have changed substantially. Moreover, ongoing sound changes have affected the pronunciation of many of the sounds that cued judgments of sexual orientation from speech. The current study examines whether these changes affect the perception of sexual orientation through speech. The perception experiments described in Munson et al. are being redone using two groups of listeners. One group is matched in age to subjects whose data were reported previously (i.e, currently 18-30 years old). The second group that is matched in birth year to the subjects from the earlier study (i.e., currently 33-45 years old). Ongoing analyses compare these new data are compared to those from Munson et al.
High performance computing methods for nonlinear Bayesian uncertainty quantification
Authors: Dettmer Jan , Dosso Stan E. , Holland Charles W.
Published: April 2018

Bayesian uncertainty quantification (UQ) for nonlinear inverse problems requires the application of numerical integration (sampling) to estimate the posterior probability density since no closed-form expressions exist. Nonlinear problems are common in geophysics, in particular, in applications of studying the seabed with sound. The computational cost of applying UQ can be daunting and we present several approaches that improve efficiency for large inverse problems. Fundamentally, Bayesian sampling includes both fine-grained parallelism in the forward model (data prediction) as well as coarse grained parallelism in the sampling. Fine grained parallelism can be addressed efficiently by implementation on massively parallel accelerators, such as graphics processing units, and application to reflection coefficient computation is shown. The coarse grained parallelism of sampling is ideally addressed by traditional parallelization with message passing across a cluster of computers. We consider implementation of parallel sampling algorithms that scale efficiently to 103 computer cores. Finally, computational efficiency is closely tied to parametrization efficiency, which is addressed by self-adapting parametrizations of unknown complexity that lead to parsimonious representations of complex environments with few parameters. These three aspects of efficiency will be illustrated for several inverse and imaging problems in seabed acoustics and seismology. [Funded by the Natural Sciences and Engineering Research Council of Canada.]
Some examples of the application of high-performance computing for time-domain full-wave simulations in underwater acoustics using a spectral-element method
Authors: Cristini Paul , Komatitsch Dimitri , Bottero Alexis
Published: April 2018

Being able to perform accurate time-domain full-wave simulations in underwater acoustics is important within the context of complex environments. Among the numerical methods that can be used to perform such types of simulations, the spectral-element method is a method of choice because it can take advantage of the possibilities offered by high-performance computing. This capability is very important because accurate numerical simulations require a high computational power. In this presentation we will show some examples of the use a spectral-element method for underwater acoustics applications. 2D simulations as well as 3D simulations will be considered for various configurations, illustrating the interest of performing such simulations. Shallow water propagation, deep water propagation as well as diffraction by objects in complex environments will be analyzed.
Finite element modeling for ocean acoustics applications using high performance computing
Authors: Isakson Marcia J.
Published: April 2018

Finite element models provide solutions to the Helmholtz equation for ocean acoustics applications, which are exact on the order of the discretization. However, to achieve convergence the discretization must be on the order of several elements per acoustic wavelength. For large-scale ocean acoustics applications, and small (high-frequency) acoustic wavelengths, the number of elements required often exceeds millions. In addition, in each element, the basis set decomposition required for finite element modeling increases the number of degrees of freedom, and for problems involving elastic structures, additional degrees of freedom are required to describe the elasto-dynamic acoustics equation. Therefore, for a large-scale ocean acoustics problem, the number of degrees of freedom can reach into the tens of millions. This requires large memory caches on computing systems. The number of degrees of freedom can be reduced by using wavenumber decomposition techniques at the expense of running many models. In this talk, large-scale ocean acoustics finite element modeling will be reviewed from an historical perspective, the current state of modeling will be discussed from the in light of available computing resources and the future of finite element modeling will be considered. [Work supported by ONR, Ocean Acoustics.]
Numerical modeling with high performance computing of seismic waves for complex marine environments: Benchmarking with laboratory experiments
Authors: Solymosi Bence , Favretto-cristini Nathalie , Monteiller Vadim , Cristini Paul , Arntsen Borge , Komatitsch Dimitri , Ursin Bjorn
Published: April 2018

Numerical simulations are widely used for forward and inverse problems in seismic exploration to investigate different wave propagation phenomena. However, the numerical results are hard to be compared to real seismic measurements as the subsurface is never exactly known. Using laboratory measurements for small-scale physical models can provide a valuable link between purely numerical and real seismic datasets. We present a case study for comparing ultrasonic data for a complex model with spectral-element and finite-difference synthetic results. The small-scale model was immersed in a water tank. Reflection data was recorded with piezoelectric transducers using a conventional pulse-echo technique. We paid special attention to the implementation of the real source signal—and radiation pattern—in the numerical domain. It involved a laboratory calibration measurement, followed by an inversion process. The model geometry was implemented using a non-structured mesh for the spectral-element simulations. The comparisons show a very good fit between synthetic and laboratory traces in general, and the small discrepancies can be assigned mostly to the noise present in the laboratory data.
Integrated ocean acoustics and dynamics modeling with computer clusters
Authors: Lin Ying-Tsong , Duda Timothy F. , Zhang Weifeng G. , Newhall Arthur
Published: April 2018

Underwater sound propagation in the ocean can be influenced by a variety of physical oceanographic processes, including ocean currents, eddies, internal gravity waves, tides, fronts, instabilities, etc. Our group at the Woods Hole Oceanographic Institution has been developing several numerical simulation frameworks to integrate ocean acoustic and dynamical models and implement them on computer clusters. Most of the current dynamical ocean models run on clusters, and we will review our integration approaches in this talk and also point out the requirement for nesting model domains and interpolations. Different parallelization schemes will be introduced to speed up a variety of acoustic numerical models, for example, ray-tracing, normal modes, couple modes and Parabolic-Equation approximation models. Examples of 3D sound propagation in a number of ocean environments (canyons, slopes, continental shelves and basins) with different dominating ocean processes will be demonstrated. Model performance improvement and limitation will be discussed. [Work sponsored by the ONR.]
Broadband numerical simulations of scattering from rough surfaces
Authors: Olson Derek R.
Published: April 2018

Numerical simulation of rough surface scattering via discretization of the Helmholtz-Kirchhoff integral equation (HKIE) is a powerful, yet computationally expensive method to study rough surface scattering. In this work, simulations are performed using Fourier synthesis of the numerical solution of the HKIE using the boundary element method (BEM). Each frequency component is solved using BEM employing a good approximation of a plane wave as an incident field. The surface length requirements on this incident field depend on angle, and all simulations are performed using plane waves whose angular width is less than one degree, and whose mean grazing angle is greater than 20 degrees. This requirement resulted in problems with over 22,000 degrees of freedom and approximately 3000 individual frequencies. This broadband technique is employed to study the dependence of the scattered intensity on surface parameters as well as the bandwidth of the transmitted pulse. Simulations are performed both on surfaces with truncated power law spectra, as well as rippled surfaces with power-law roughness superimposed.
Sound radiation from a cylinder in shallow water by FEM and PE method
Authors: Qian Zhiwen , Shang Dejiang , He Yuanan
Published: April 2018

There is no reliable research method for the acoustic radiation prediction of elastic structures in shallow water at present. Based on the finite element method coupled with the parabolic equation, the theoretical model for structure acoustic radiation in shallow water in low frequency is established in this paper. The vibro-acoustic characteristics of elastic cylinder influenced by with upper and lower fluid boundaries is calculated and analyzed. The study shows that when the cylindrical shell approaches the sea surface or bottom, the coupled frequency is higher or lower respectively than that of the shell immersed in the free field. When the diving depth reaches a certain distance range, the coupled frequency tends to be the same as that in free field. The acoustic field radiated from an elastic shell in Pekeris waveguide is similar to that from a point source in low frequency, but significant differences exist between them in high frequency. The structural source can’t be equivalent to a point source. The research results also show that the method proposed in this paper has good adaptability to the type of structure geometry and shallow water waveguide, and the calculation efficient and accurate are also very high.
The effects of high intensity focused ultrasound on biofilms formed by Pseudomonas aeruginosa
Authors: Bharatula Lakshmi D. , Marsili Enrico , Rice Scott , Kwan James J.
Published: April 2018

Bacterial infections are increasingly difficult to treat due to their growing resistance to antibiotics. Most of these bacterial infections form a biofilm that limits the effectiveness of the antibiotic. Biofilms are microbial cells that are protected by a self-generated matrix of extracellular polymeric substances. In addition to their intrinsic antibiotic resistance, these biofilms are able to respond to the stresses from the antibiotic by inducing drug resistance mechanisms. Currently, the strategy to combat drug resistance is to develop novel drugs, however, the rate of drug development is being surpassed by the rate of drug resistance. There is therefore a need for alternative means in enhancing the efficacy of current drug therapeutics. We propose to use of high intensity focused ultrasound (HIFU) to disrupt the biofilm and promote drug penetration. However, the effects of HIFU on these bacterial communities remain unknown. Here we report on microstructural changes within biofilms formed by Pseudomonas aeruginosa due to exposure to HIFU at 500 kHz center frequency. Changes to the biofilm were nondestructively measured through impedance spectroscopy and confocal microscopy. Biofilms were shown to induce cavitation (as measured by a passive cavitation detector) at relatively low pressure amplitudes suggesting the presence of cavitation nuclei within the extracellular matrix.
In situ hydrogel formation for biomedical applications using acoustic cavitation from high intensity focused ultrasound
Authors: Jonnalagadda Umesh , Li Feifei , Lee Jim , Goto Atsushi , Nguyen Minh , Kwan James J.
Published: April 2018

There is a growing interest in polymer mechanochemistry for their industrial applications. For example, stress-induced crosslinking gel formation from polymer networks is a rapidly growing field of study. Recent work utilizes a variety of different polymer structures and crosslinking mechanisms. However, these polymers are typically soluble in only organic solvents and require the use of a sonicating probe or bath at frequencies below 100 kHz. These requirements limit their use in biomedical applications that require in situ gel formation within a patient (e.g., blocking of varicose veins, internal wound healing, etc.). Here we report on the development of a water soluble block copolymer that forms a hydrogel in the presence of acoustic cavitation from high intensity focused ultrasound. These block copolymers are comprised of hydrophilic polyethylene glycol methyl methacrylate units and hydrophobic tridentate crosslinkers. The tridentate crosslinker forms bonds with free metal ions in solution only in the presence of acoustic cavitation induced mechanical stress. We show that the block copolymer is capable of forming a hydrogel in under 90 seconds and will also block a liquid channel formed in an agarose cylinder.
Blood coagulation monitoring using acoustic levitation
Authors: Ansari Vahideh , Brugnara Carol , Holt R. G.
Published: April 2018

Impaired blood coagulation can result from a variety of conditions including severe trauma, illness or surgery, and can cause life-threatening bleeding or thrombotic disorders. As a result, instruments which measure functional changes in blood properties upon activation of the clotting cascade are crucial to assess coagulopathies in various disease states. Thromboelastography (TEG) is the gold standard for whole blood coagulation monitoring. TEG requires the blood to be in contact with the sample holder and sensor, leading to a variety of potential artifacts in the results. Acoustic levitation provides non-contact containment and manipulation. We have levitated microliter drops of blood, and employed a drop eigenmodal oscillation technique in order to infer viscoelastic material properties of blood as it coagulates. By comparing our results with TEG results on the same samples, we are able to illustrate certain advantages of the levitation technique. [Work supported by NSF grant # 1438569.]
Exploiting Ballou’s rule for better tissue classification
Authors: Kvam Johannes , A. J. Angelsen Bjørn , Holm Sverre
Published: April 2018

Tissue characterisation using the parameter of nonlinearity B/A has shown promising diagnostic value in medical imaging. Its estimation usually infers an assumption of constant sound speed and density. However, an empirical result known as Ballou’s rule shows a significant correlation between the reciprocal sound speed and the parameter of nonlinearity for liquid metals. Since the 60’s, this result has been found also to be applicable for soft tissues as well with a high correlation (r = 0.83). The correlation between B/A and compressibility, the inverse bulk modulus, is just as strong (r ≥ 0.83) indicating that the product of the two can be beneficial for two main reasons. First, as the variables are highly correlated the variation in the product is larger than that of B/A by itself. This allows for a higher sensitivity as the separation between tissue types will be larger. Second, as methods for estimating B/A often assume constant sound speed and density, variations in these parameters result in uncertainty in the estimated B/A values. By estimating the product of B/A and compressibility instead, the accuracy of the estimate improves. There are multiple methods for estimating this product including the dual frequency SURF method (Hansen et al., JASA 2010).
High-frequency (10-100 MHz) ultrasound instrumented forceps for precision cancer surgery
Authors: Doyle Timothy E. , Salisbury Michael J. , Bennett Michael J. , Wagner Garrett , Carter Caitlin , Gunter Tobee P. , Carlson Jessica E. , Cowan Nicole , Gay Johnathon S. , Matsen Cindy B.
Published: April 2018

A critical issue for surgery of soft tissue cancers is ensuring removal of all malignant tissue while conserving as much unaffected tissue as possible. A minimally invasive, in vivo technique for detecting residual cancer in surgical margins or metastatic cancer in lymph nodes would significantly improve the precision and efficacy of cancer surgery. The objective of this project was to develop ultrasound instrumented “smart” forceps to guide surgeons during operations, to provide instant diagnostic information, and to enable more precise and complete resection of malignant tissue. The device was based on Martin forceps, modified to include two ultrasonic sensors (polyvinylidene difluoride) at the tips of the forceps, a tissue thickness sensor (rotary potentiometer), sensor wires, and a spring to control the manual stiffness of the forceps. A high-frequency pulser-receiver was used to excite the transmitting sensor at 50 MHz and amplify through-transmission signals from the receiving sensor. The forceps were tested with agarose phantoms embedded with polyethylene microspheres of different diameters (58-550 μm) to vary attenuation. Testing included standard 50-MHz immersion transducers for comparison. The results showed that the forceps’ performance was equal to standard transducers, with comparable sensitivity for attenuation and superior accuracy for wave speed.
Gas-generating nanoparticles for molecular ultrasound imaging
Authors: Sun In-Cheol , Emelianov Stanislav
Published: April 2018

Diagnostic ultrasound imaging often relies on contrast agents. Most common contrast agents are microbubbles that are confined to vascular compartments and molecular targets because micrometer size particles cannot escape through endothelial barriers. Therefore, a desired ultrasound contrast agent should consist of nanometer scale particles that are capable of escaping from vasculature, penetrating into tissue, and then generating sufficient contrast once they reach the target site. We developed a novel contrast agent—plasmonic nanoparticles covered by azide compounds (AzNPs), capable of on-demand laser-induced gas generation via photolysis of azide functional groups. The 50 nm diameter AzNPs were small enough to penetrate the endothelial barrier. Upon laser activation, the AzNPs generated nitrogen gas which served as ultrasound contrast agent. The feasibility of the AzNPs to produce ultrasound contrast was tested within polyethylene tube under laminar flow. Upon laser irradiation, significant ultrasound signal enhancement was observed due to the N2 gas bubbles generated by the photolysis of AzNPs. These and other studies suggest that the AzNPs may enable the ultrasound diagnosis of various diseases that conventional microbubbles cannot detect. Furthermore, these optically absorbing particles can also be used for imaging and therapeutic applications of light and sound such as ultrasound-guided photoacoustic imaging.
Plane-wave vector-flow imaging of adult mouse heart
Authors: Ketterling Jeffrey A. , Shekhar Akshay , Aristizabal Orlando , Podkowa Anthony , Yiu Billy Y. , Yu Alfred
Published: April 2018

High-frequency ultrasound Doppler modes have been used extensively for murine cardiovascular (CV) studies, but traditional linear-array imaging modes are limited in terms of spatial and temporal resolution. Plane-wave imaging methods allow for high-speed vector-flow information to be obtained throughout a full image frame. Plane-wave imaging has been demonstrated in human CV studies, but its use in mouse models has received minimal attention. A Verasonics Vantage with an 18-MHz linear array was used to acquire plane-wave data at a frame rate of 30 kHz from the left ventricle of adult mice. Batches of 3 transmissions spanning ± 5 degrees were sent out. The mouse was placed supine on a heated imaging platform and then 2D + time data sequences. The data were beamformed using standard delay-and-sum methods and vector-flow estimates were obtained at each pixel location using a least-squares, multi-angle Doppler analysis approach. Vortex patterns in the left ventricle were visualized over several heart cycles showing the complex flow in the mouse heart.
Using mean frequency estimation algorithms for unambiguous identification and visualization of an acoustically active catheter
Authors: Kumar Viksit , Kim Bae Hyeong , Alizad Azra , Belohlavek Marek , Fatemi Mostafa
Published: April 2018

Minimally invasive procedures using ultrasound are becoming prominent, especially in applications like biopsy, catheter guidance, and surgeries. In our previous work a catheter tip is fitted with a miniature omnidirectional piezoelectric crystal; the ultrasonic field from the imaging array and the piezoelectric crystal interact resulting in a symmetric Doppler shift. Previously, a frequency domain algorithm was used to identify pixels having the symmetric Doppler shift. The identified pixels can then be visualized on B-mode and color map with a unique color thus representing the location of the catheter tip. However, frequency domain algorithms are computationally expensive and require changes to data workflow. Using mean frequency estimators with symmetric Doppler shift results in the catheter tip being displayed as zero mean noise making it hard to distinguish from color Doppler noise. To overcome this limitation, complex demodulation can be used. Modulating the time domain signal with sine and cosine by the piezoelectric excitation frequency and summing them up results in cancellation of one of the symmetric Doppler components. With only one frequency component remaining mean frequency estimators can be used to identify the location of the catheter. The presented algorithm has lower computational complexity and requires minimal change in software design.
Modeling element directivity in minimum variance beamforming for medical ultrasound
Authors: Tracey Brian H. , Lemmerhirt David , Penninck Dominique , Polak Joseph F.
Published: April 2018

Minimum variance (MV) adaptive beamforming, which adaptively estimates and suppresses interfering signals, has attracted increased attention for ultrasound imaging in recent years. While many MV algorithms have been applied to ultrasound, these algorithms generally rely on signal models that neglect amplitude differences across the array due to element directivity or other factors, introducing mismatch for near-array sources. This paper proposes a beamspace method using randomly sampled subarrays which allows the use of higher-fidelity signal models. Using experimental data, we demonstrate that this algorithm yields noticeable gains in signal contrast by accounting for element directivity.
Repurposing the algorithm: How digital signal processing brought on the re-use of reverb
Authors: Deshpande Nikhil , Braasch Jonas
Published: April 2018

The earliest digital reverberation algorithms were designed to provide sound with a wider and more immersive sense of physical time-based space. These algorithms successfully replicated the perceptual attributes of realistic rooms, but there was also an interesting and perhaps unforeseen secondary outcome. The ubiquity of digital reverberation made the creative misuse of these algorithms to construct physically impossible spaces readily accessible to musicians. By providing users with access to algorithm controls, reverb grew from a tool for constructing realistic perceptions of rooms into the creation of sound design—and often, the centerpiece of composition. Rather than provide a perceptually accurate presentation of sounds in a stereo field, artists instead began to approach reverb as a smaller part of larger timbral systems. Examples span from reverse reverb to the more complex Eno-based shimmer system, and reverb’s place in production and perception will be considered and discussed.
Effects created by time-variant spectral processing of sounds
Authors: Beauchamp James W.
Published: April 2018

Various processes can be used to modify a sound to produce special effects. One approach is to first compute a time-frequency represention of a sound signal, follow that by altering the representation in various ways, and finally perform resynthesis to produce modified versions of the signal. Example modifications are (1) duration modification (time-scaling), (2) pitch change, (3) noise content manipulation, (4) spectral envelope modification, and (5) temporal envelope modification. The time-frequency representation can also be used to develop simplified synthesis models that depend on only a few time-varying parameters, such as overall amplitude, pitch, and spectral centroid and shape. In the special case of musical sounds with vibrato, spectral amplitudes and frequencies can be parameterized in terms of time-variant vibrato depth, rate, and mean envelope. These parameters can then be controlled independently of pitch and duration. Also, timbral parameters of instruments can be interchanged or blended to create hybrid instruments with novel timbral qualities. Several of these effects will be described and demonstrated.