Preston S. Wilson

Hemp (Cannabis sativa) seed oil is recognized as a valuable oil due to its beneficial fatty acid profile, which includes a favorable balance of omega-6 and omega-3 fatty acids, making it highly desirable for edible and bioproduct applications. Crude hempseed oil contains high concentrations of chlorophyll, carotenoids, and other amphiphilic compounds that can negatively affect its appearance, stability, and downstream processing. Therefore, bleaching is a crucial step in removing these pigments after the degumming and neutralization processes. To optimize the bleaching process, a Box–Behnken response surface methodology was employed, focusing on three factors: time (15, 30, 45 min), temperature (100, 120, 140 °C), and bleaching earth concentration (2.5, 5, and 7.5% w/w). The key response variables were β-carotene, chlorophyll content, and antioxidant activity. For chlorophyll removal, bleaching earth concentration accounted for 83.82% and 81.84% of the variation in the solvent-extracted and mechanically extracted oils, respectively. For β-carotene, the bleaching earth concentration accounted for over 93% of the variation in both types of oil. The optimal bleaching earth concentrations were determined to be 4.87% and 5.36% for the solvent-extracted and mechanically extracted oils, respectively, to achieve the target chlorophyll level of ≤150 ppb. Mechanically extracted oil had lower antioxidant activity after bleaching compared to solvent-extracted oil. The addition of bleaching earth, up to 5%, removed polar antioxidants, further lowering the oil’s antioxidant capacity. These findings suggest that optimizing bleaching conditions can significantly affect both pigment removal and the antioxidant profile of the final product.

Studies of acoustic propagation in seagrass meadow environments have demonstrated a high degree of sensitivity of passive and active acoustics to diurnal photosynthetic cycles and seasonal growth patterns. While empirical metrics based on these measurements in combination with traditional ecological monitoring methods provide insight into trends in primary productivity, estimates of seagrass biomass and other ecological condition indicators have not yet been calculated directly from acoustic measurements. Towards this goal, an acoustic inference was developed utilizing a Bayesian framework to infer estimates of seagrass biomass. This work was based on active acoustic measurements collected over the course of a 25-month remote monitoring experiment conducted in a seagrass meadow in a shallow-water sub-tropical estuary. A ray-based acoustic propagation model was developed to incorporate effects of the seagrass leaf canopy and model parameter estimates related to the height and leaf density of the canopy are used to predict above-ground seagrass biomass over the course of the experiment. The study found biomass to be consistent with seasonal trends found in previous measurements. Comparison of acoustic estimates with an 11-month record of direct measurements of biomass shows good agreement, demonstrating the potential of acoustic inversion to facilitate acoustic-based ecosystem monitoring in seagrass meadow environments.

Over the past decade, an interdisciplinary team of scientists conducted a series of at-sea measurements designed to further our understanding of acoustics in complex ocean environments. Most of these efforts focused on bottom-interacting acoustics in areas characterized by fine-grained sediments. Geographically, the primary experimental sites and data analysis took place in an area of the Western Atlantic Ocean approximately 60 miles south of Martha's Vineyard, MA, known as the New England Mudpatch, and extending south to include the shelf break and upper slope characterized by larger-grained sediments. This introductory paper provides a summary of the various experimental techniques and analysis approaches detailed in the collection of 23 papers that make up this special issue focused on Assessing Sediment Heterogeneity on Continental Shelves and Slopes.

This paper considers the information content for seabed geoacoustic inversion of recorded acoustic waveforms processed as modal-dispersion (MD) data (mode arrival times as a function of frequency) and matched-field (MF) data (multifrequency complex acoustic fields across a sensor array). These approaches are applied separately and combined in joint inversion, where the MD and MF data sets are derived from the same acoustic recordings collected during the 2017 Seabed Characterization Experiment on the New England Mud Patch. Unlike MD inversion, MF inversion requires knowledge of source and receiver depths, and the complex source spectrum must be estimated as part of the inversion. However, MF inversion is sensitive to seabed attenuation (MD is not) and more easily extended to higher frequencies, where mode filtering for MD data is challenging. Comparison of geoacoustic information content is facilitated here using trans-dimensional Bayesian inversion to sample probabilistically over the number of layers of the seabed model as well as the order of an autoregressive error model. Results indicate MF inversion resolves more detailed geoacoustic structure with smaller uncertainties, including good estimates of the attenuation profile for wideband (20-1504 Hz) inversions.

Transcranial focused ultrasound is a promising non-invasive method for neuromodulation, particularly for neurodegenerative and psychiatric conditions. However, its use in wearable systems has been limited due to bulky devices and reliance on ultrasound gel, which dehydrates and lacks stable adhesion for long-term use. Here, we present a miniaturized wearable ultrasound device, comparable in size to standard electrophysiological electrodes, integrated with a bioadhesive hydrogel for stable, long-term somatosensory cortical stimulation. Our air-cavity Fresnel lens based self-focusing acoustic transducer was fabricated via a lithography-free microfabrication process, achieving 30.7 W/cm² (1.92 MPa) acoustic intensity and 10 mm focal depth. The hydrogel couplant exhibited less than 13% acoustic attenuation and maintained a stable adhesion force of 0.961 N/cm for 35 days. Using this system, we successfully suppressed somatosensory evoked potentials elicited by functional electrical stimulation over 28 days, demonstrating the device’s potential for long-term, wearable neuromodulation applications. Transcranial focused ultrasound can be used for neuromodulation, but its use in wearable systems remains challenging. The authors present a miniaturised wearable ultrasound device, integrated with a bioadhesive hydrogel for stable, long-term somatosensory cortical stimulation.

This Letter estimates shear and compressional seabed geoacoustic profiles at the New England Mud Patch through trans-dimensional Bayesian inversion of matched-field acoustic data over a 20-2000 Hz bandwidth. Results indicate low shear-wave speeds (∼35 m/s) with relatively small uncertainties over most of the upper mud layer, increasing in underlying transition and sand layers. Compressional parameters, including attenuation, are also well estimated, but shear-wave attenuation is poorly determined. Comparison of inversions with/without shear parameters and consideration of inter-parameter correlations indicate that estimates of compressional parameters are not substantially influenced by shear effects, with the possible exception of compressional-wave attenuation in the sand layer.

This paper estimates depth-dependent profiles of shear- and compressional-wave geoacoustic properties for seabed sediments at the New England Mud Patch through matched-field inversion of broadband (20-2000 Hz) acoustic data recorded at a 14-element vertical line array due to a combustive sound source. Trans-dimensional Bayesian inversion is applied to sample probabilistically over the number of seabed layers and corresponding layer depths and geoacoustic properties, as well as over the order and parameters of an autoregressive error model. This approach, based on a parallel-tempering implementation of birth/death reversible-jump Markov-chain Monte Carlo sampling, combines objective, data-driven model selection and quantitative parameter/uncertainty estimation. Results indicate low shear-wave speeds (∼30 m/s) with small uncertainties over most of the upper mud layer, increasing in underlying transition and sand layers, with values in good agreement with in situ probe measurements (for the mud) and nominal values (for sand). The compressional-wave attenuation profile is well estimated but shear-wave attenuation is poorly constrained. Comparison of results for inversions both with and without shear-wave parameters and consideration of inter-parameter correlations indicate that estimates of compressional-wave parameters, including attenuation, are not substantially influenced by shear-wave effects, with the possible exception of the sand layer.

Noise from calving icebergs, cracking ice, and melting ice dominate the underwater soundscape of glacierized fjords. The combination of these sources results in one of the loudest recorded ambient ocean environments. Until now, the combined symphony of sounds has made identifying specific sources difficult, limiting its value to provide insights into the physical processes influencing ice-ocean interactions. Here, we show that unsupervised machine learning can separate the signal into five dominant sound profiles related to glacier activity. For this work, we deployed an array of hydrophones approximately 400 m from the terminus of Xeitl Sít’ (LeConte Glacier) in Southeast Alaska and recorded sound at regular intervals between October 2016 and May 2017. Using the k-means clustering algorithm, we cluster spectral shapes of 10,440 background acoustic spectra, defined as the 25th-percentile spectral level of each recording. We identify five distinct acoustic clusters and associate their temporal occurrence with environmental time series including ice movement, local meteorological conditions, and oceanographic data. We further associate the spectral shape and audio signals to known glacier sources such as calving and ice melt. Our analysis reveals that these acoustic clusters correspond more closely with glacier and ice-mélange activity than other environmental variables, confirming the dominance of glacier behavior on fjord soundscapes. This research demonstrates the straightforward application and effectiveness of clustering passive acoustic data and sets a foundation for using soundscapes to monitor and detect environmental changes in glacierized fjords.

Benthic biological processes influence seabed heterogeneity and contribute to variability in geoacoustic properties. To investigate these relationships, measurements were conducted to quantify spatial variability in the upper few decimeters of sediment near the water-seabed interface within a fine-grained sediment deposit on the New England continental shelf. At each measurement location, an acoustic multicorer was deployed to sample the seabed. Acoustic probes were inserted into the sediment to collect direct in situ measurements of sediment compressional wave speed and attenuation (30-100 kHz) under near-ambient conditions, after which cores were collected from the inter-probe propagation paths. Sediment physical properties, organic carbon, infaunal community composition, and ex situ compressional wave speed and attenuation spanning two frequency decades (104-106 Hz) were subsequently measured in the laboratory. The frequency dependence of sound speed ratio and attenuation was analyzed in the context of sediment acoustics models for mud based on the viscous grain shearing and extended Biot models. Sites with greater abundance of larger-bodied infauna (>1 mm) displayed higher variability in sound speed and attenuation. Correlation was found between sediment compressional wave modulus and total organic carbon, suggesting that organic matter in the sediment matrix also affects bulk acoustic properties.

Oxygen ebullition is typically ignored in long-term measurements of net ecosystem productivity (NEP), which reflects whether systems are net heterotrophic or autotrophic based on diel changes in oxygen. The solubility of oxygen in seawater is a function of temperature, salinity, and pressure. Warm, high-salinity seawater has low oxygen solubility, and when combined with the photosynthetic productivity of macrophytes in shallow, clear waters, oxygen ebullition frequently occurs. The presence of mixed-phase oxygen in supersaturated seawater creates difficulties for oxygen measurements because sensors cannot measure dissolved and gas phases simultaneously. Therefore, dissolved oxygen measurements must be taken in conjunction with separate ebullition measurements to develop an accurate oxygen budget needed to characterize NEP. Here, we seek to understand the drivers of NEP for a Thalassia testudinum meadow in the Gulf of Mexico and calculate ebullition rates using acoustic sensing. We hypothesize that oxygen ebullition will substantially increase NEP, particularly during the summer months because of photosynthetic dependence on temperature and irradiance. We found that the seagrass meadow is typically oxygen saturated during the hours 0700 to 2200 with maximum saturation occurring at 1400. Acoustic-based methods and general additive modeling both found highest ebullition rates in July/August. High respiration led to an apparent net heterotrophic system (NEP = −2.1 mmol O 2 m −2 d −1 ), but accounting for air–sea exchange and ebullition causes the system to be autotrophic (NEP = 54 mmol O 2 m −2 d −1 ). This study demonstrates the importance of including ebullition into NEP calculations and the viability of acoustics as a tool for monitoring aquatic productivity.

Highlights The phospholipid and chlorophyll amounts were significantly different in the mechanical and solvent extracted oils. Water degumming was sufficient in removing phospholipid in the mechanically extracted oil. The type of acid used did not influence the amount of phospholipid removed in solvent extracted oil. The same amount of sodium hydroxide was needed during neutralization since the free fatty acid values were not significantly different after extraction. Abstract. Crude hemp (Cannabis sativa) seed oil is highly pigmented due to the presence of chlorophylls, carotenes, and other antioxidants, which can potentially hinder downstream processes, rendering it undesirable for food and bioproduct applications. The composition and quantity of impurities in hempseed oil are likely influenced by the oil extraction method. Therefore, this study aimed to identify the optimal chemical refining conditions for mechanical and solvent extracted oils and compare the quality of the refined oil. Crude oils were obtained through two extraction methods: cold pressing using a Komet twin-screw for mechanical extraction and solvent extracted oil using hexane in a 12 L Soxhlet extraction unit. Subsequently, the crude oils underwent degumming with citric and phosphoric acids at three acid concentrations, followed by neutralization at varying sodium hydroxide concentrations. The efficacy of the refining conditions was assessed by measuring the phospholipid and free fatty acid contents. The results revealed that the phospholipid content of the crude solvent extracted oil was ten times higher than that of the mechanically extracted oil. Consequently, the solvent extracted oil required approximately three times the amount of acid to reach the target of <15 ppm residual phospholipids. Interestingly, the type of acid used did not influence the refining process of hempseed oil. These findings suggest that the oil extraction method significantly influences the refinement process required to meet the industrial threshold of vegetable oil containing =15 ppm phospholipids. Keywords: Free fatty acid, Hempseed oil, Phospholipids, Refined vegetable oil, Vegetable oil extraction.

This article presents a spatial environmental inversion scheme using broadband impulse signals with deep learning (DL) to model a single spatially-varying sediment layer over a fixed basement. The method is applied to data from the Seabed Characterization Experiment 2022 (SBCEX22) in the New England Mud-Patch (NEMP). Signal Underwater Sound (SUS) explosive charges generated impulsive signals recorded by a distributed array of bottom-moored hydrophones. The inversion scheme is first validated on a range-dependent synthetic test set simulating SBCEX22 conditions, then applied to experimental data to predict the lateral spatial structure of sediment sound speed and its ratio with the interfacial water sound speed. Traditional geoacoustic inversion requires significant computational resources. Here, a neural network enables rapid single-signal inversion, allowing the processing of 1836 signals along 722 tracks. The method is applied to both synthetic and experimental data. Results from experimental data suggest an increase in both absolute compressional sound speed and sound speed ratio from southwest to northeast in the NEMP, consistent with published coring surveys and geoacoustic inversion results. This approach demonstrates the potential of DL for efficient spatial geoacoustic inversion in shallow water environments.

The bleaching process is aimed at removing pigments, traces of metals, and residual phospholipids to improve the color, stability, and quality of the oil. Distillers corn oil (DCO) contains lots of β-carotene that are beneficial but no study has focused on optimizing the removal of pigments while minimizing the loss of β-carotene. Hence, a response surface methodology with the Box-Behnken design was used to study the effect of the process parameters during bleaching. The process parameters were dosage of bleaching clay (1 − 3%), time (5 − 25 min), and temperature (90 − 110 ºC) for neutralized DCO on the laboratory scale. The optimal parameters were bleaching clay dosage of 1.2%, time of 23.2 min, and temperature of 99.1 °C. The β-carotene reduced from 0.2% − 36%, red color reduced from 27% − 88%, and yellow color reduced from 0% − 83%. The PV values of the bleached oil sample ranged from 1.7 to 9.4 meq O 2 /kg. The quality of DCO at the optimal bleaching level was compared with conventional edible corn oil. The models developed was used to identify the precise balance between enhancing color removal and maintaining beneficial nutritional values. • The optimized bleaching conditions of distillers’ corn oil (DCO) was shown to reduce 30−45% of beaching clay usage and approximately 50% of the bleaching time. • The bleaching clay dosage had the most considerable impact (>50%), followed by time (13−18%) and temperature (7−12%). • The quality of the bleached DCO was comparable with that of food-grade corn oil (corn germ oil).

Seagrasses provide a multitude of ecosystem services and act as important carbon sinks. However, seagrass habitats are declining globally, and they are among the most threatened ecosystems on earth. For these reasons, long-term and continuous measurements of seagrass parameters are of primary importance for ecosystem health assessment and sustainable management. This paper presents results from both active and passive acoustical methods for ecosystem monitoring in seagrass meadows. From a propagation perspective, gas bodies contained within the seagrass tissue as well as photosynthetic-driven bubble production result in attenuation, dispersion, and scattering of sound that produce increased transmission loss. For the passive approach, the detachment of gas bubbles from the plants is an important component of the ambient soundscape. Examples of both techniques will be presented based on data collected as part of a two-year continuous deployment of an acoustical measurement system operating in a moderately dense seagrass bed dominated by Thalassia testudinum (turtle grass) in Corpus Christi Bay, Texas. The data show annual trends related to the seasonal growth pattern of Thalassia as well as diurnal trends correlated with photosynthetically active radiation.

This paper reports on an original set of direct sound speed measurements collected with the acoustic coring system in the New England Mud Patch (NEMP) and shelf break area to the south. Cores collected within the NEMP show range-dependence of the mud with slower sound speed and lower attenuation on the west side. In the shelf break region, the highest sound speeds are observed between the 200- and 350-m isobaths. The depth-dependence of the mud layer in the NEMP includes a surficial layer with a negative sound speed gradient of 28 s-1. The remainder of the mud column has a weak positive sound speed gradient of 6.2 s-1 over an isovelocity layer. Comparison between in situ and ex situ sound speed measurements provides an assessment of the effects of sediment disturbance from gravity coring operations. Small differences in the upper 2.5 m were attributed to the changes in the geoacoustic properties caused by disturbance from the coring process. Below 2.5 m, the average difference is close to zero, suggesting that these sediments were minimally disturbed. Finally, an in situ measurement of shear speed was obtained near the depth of maximum penetration. The shear speed was well correlated with sound speed from approximately the same depth interval.

The very low-frequency noise from merchant ships provides a good broadband sound source to study the deep layers of the seabed. The nested striations that characterize ship time-frequency spectrograms contain unique acoustic features corresponding to where the waveguide invariant β becomes infinite. In this dataset, these features occur at frequencies between 20 and 80 Hz, where pairs of modal group velocities become equal. The goal of this study is to identify these β = ∞ frequencies in ship noise spectrograms and use them to perform statistical inference for the deep layer sound speeds and thicknesses in the New England Mudpatch for a larger number of ships and acoustic arrays over a larger geographical region than previously studied. Marginal probability distributions of the data indicate that using singular points for a feature-based inversion yields an estimate of the sound speed and a limiting value for the thickness of the first deep layer. Heterogeneity is examined by correlating spatial variability of the deep layer sound speeds with ship tracks.

The acoustical oceanography (AO) curriculum at The University of Texas at Austin (UT) consists a number of courses and thesis research, which often includes field work. The core course is EE/ME 384N-5, Underwater Acoustics, which covers acoustic properties of the ocean, propagation, reflection, reverberation, scattering and target strength, ocean noise, array and signal processing and basic sonar design. The course is offered in alternate years and is cross-listed as both an electrical and mechanical engineering course. Prior to this, students usually take two semesters of physical acoustics: EE/ME 384N-1 and 2, Acoustics I and II, which covers plane waves in fluids, transient and steady-state reflection and transmission, lumped elements, refraction, ray acoustics, absorption and dispersion, spherical and cylindrical waves, radiation and scattering, multipole expansions, Green’s functions, waveguides, Fourier acoustics, and Kirchhoff theory of diffraction. Both are offered every year. Another course commonly taken by AO students is EE/ME 384N-3: Electromechanical Transducers, which covers basic modeling, analysis and design of acoustics and vibration transducers, including calibration. Recent student thesis topics have included marine acoustic ecology, the investigation of methane seeps, acoustic seagrass monitoring, and the assessment of glacial processes. Appropriate courses in UT’s natural and earth sciences departments supplement the acoustics courses.

Background: Bioacoustic monitoring is an effective and minimally invasive method to study wildlife ecology. However, even the state-of-the-art techniques for analyzing birdsongs decrease in accuracy in the presence of extraneous signals such as anthropogenic noise and vocalizations of non-target species. Deep supervised source separation (DSSS) algorithms have been shown to effectively separate mixtures of animal vocalizations. However, in practice, recording sites also have site-specific variations and unique background audio that need to be removed, warranting the need for site-specific data. Methods: Here, we test the potential of training DSSS models on site-specific bird vocalizations and background audio. We used a semiautomated workflow using deep supervised classification and statistical cleaning to label and generate a site-specific source separation dataset by mixing birdsongs and background audio segments. Then, we trained a deep supervised source separation (DSSS) model with this generated dataset. Because most data is passively-recorded and consequently noisy, the true isolated birdsongs are unavailable which makes evaluation challenging. Therefore, in addition to using traditional source separation (SS) metrics, we also show the effectiveness of our site-specific approach using metrics commonly used in ornithological analyses such as automated feature labeling and species-specific trilateration accuracy. Results: Our approach of training on site-specific data boosts the source-to-distortion, source-to-interference, and source-to-artifact ratios (SDR, SIR, and SAR) by 9.33 dB, 24.07 dB, and 3.60 dB respectively. We also find our approach allows for automated feature labeling with single-digit mean absolute percent error and birdsong trilateration accuracy with a mean simulated trilateration error of 2.58 m. Conclusion: Overall, we show that site-specific DSSS is a promising upstream solution for wildlife audio analysis tools that break down in the presence of background noise. By training on site-specific data, our method is robust to unique, site-specific interference that caused previous methods to fail.

Abstract Transcranial focused ultrasound has become a promising non-invasive approach for neuromodulation applications, particularly for neurodegenerative diseases and psychiatric illnesses. However, its implementation in wearable neuromodulation has thus far been limited due to the devices’ large size, which needs external supporting systems for the neuromodulation process. Furthermore, the need for ultrasound gel for acoustic coupling between the device and skin limits the viability for long-term use, due to its inherent susceptibility to dehydration and lack of adhesiveness to form a stable interface. Here, we report a wearable miniaturized ultrasound device with size comparable to standard EEG/ECG electrodes integrated with bioadhesive hydrogel to achieve efficient acoustic intensity upon ultrasound stimulation for long-term, wearable primary somatosensory cortical stimulation. Specifically, air-cavity Fresnel lens (ACFAL) based self-focusing acoustic transducer (SFAT) was fabricated using a lithography-free microfabrication process. Our transducer was able to achieve an acoustic intensity of up to 30.7 W/cm 2 (1.92 MPa) in free-field with a focal depth of 10 mm. Bioadhesive hydrogel was developed to address the need for long-term stability of acoustic couplant for ultrasound application. The hydrogel demonstrated less than 13% attenuation in acoustic intensity and stable adhesion force of 0.961 N/cm over 35 days. Leveraging our bioadhesive hydrogel-integrated wearable ultrasound transducer, we were able to suppress somatosensory evoked potentials elicited by median nerve stimulation via functional electrical stimulation over 28 days, demonstrating the efficacy of our transducer for long-term, wearable neuromodulation in the brain.

Data from Seabed Characterization Experiment (SBCEX-2022) conducted at the New England Mud Patch (NEMP) off the United States East Coast are analyzed in this study. Broadband Signal, Underwater Sound (SUS) sources were deployed as part of this experiment. Acoustic pressure and three components of particle motion from the SUS deployments were measured on seismic sensor packages (OBX). Polarization analysis using Stokes parameter framework is carried out to highlight the transverse components. The sensitivity of one of the Stokes parameters to modal attenuation is also investigated. Preliminary results, which compare well with previous studies, are also presented.

This paper presents inversion results for three datasets collected on three spatially separated mud depocenters (hereafter called mud ponds) during the 2022 Seabed Characterization Experiment (SBCEX). The data considered here represent modal time-frequency (TF) dispersion as estimated from a single hydrophone. Inversion is performed using a trans-dimensional (trans-D) Bayesian inference method that jointly estimates water-column and seabed properties along with associated uncertainties. This enables successful estimation of the seafloor properties, consistent with in situ acoustic core measurements, even when the water column is dynamical and mostly unknown. A quantitative analysis is performed to (1) compare results with previous modal TF trans-D studies for one mud pond but under different oceanographic condition, and (2) inter-compare the new SBCEX22 results for the three mud ponds. Overall, the estimated mud geoacoustic properties show no significant temporal variability. Further, no significant spatial variability is found between two of the mud ponds while the estimated geoacoustic properties of the third are different. Two hypotheses, considered to be equally likely, are explored to explain this apparent spatial variability: it may be the result of actual differences in the mud properties, or the mud properties may be similar but the inversion results are driven by difference in data information content.

Commercially available underwater acoustic recorders have become commonplace tools in ocean-acoustics research, due to their ease of deployment, compact size, and relatively low cost. The size of these systems typically results in a configuration with the hydrophone in close proximity to the electronics housing, flotation devices, and other equipment that can degrade the generally assumed omnidirectional response of the hydrophone. The mid-frequency acoustic regime (0.5–10 kHz) is particularly affected due to the similarity between the length-scales of these structures and the corresponding acoustic wavelengths. Calibration measurements made at an open-water test facility with a calibrated source/receiver pair characterized the frequency-dependent receiver directivity for three underwater recording devices with different housings and hydrophones: the PVC air-filled Loggerhead Snap, PVC oil-filled SoundTrap ST300, and titanium air-filled SoundTrap ST600. Furthermore, directivity measurements of a TOSSIT mooring [Zitterbart et al., HardwareX (2022)] were taken with the SoundTrap ST300 and SoundTrap ST600. Results suggest the frequency-dependent acoustic directivity of the recorders should not be neglected. In particular, the Loggerhead Snap had variations in receive level of over 20 dB as a function of receiver orientation angle and frequency, introducing a bias that obscures spectral levels of the in situ environment.

In the field of cryopreservation, there exists a class of substances known as cryoprotectant agents (CPAs), which display an ability to vitrify. These CPAs are used to prevent cellular damage during the preservation of human tissues. In a vitrified state, cells exist in a glass-like state, meaning there is no formation of mechanically damaging ice crystals during cryogenic freezing and thawing. Although a CPA’s ability to vitrify increases with concentration, its toxicity limits viable levels of use. This work seeks to find a correlation between acoustic properties of various CPAs and their concentrations via analyses of cavitation noise and cavitation jets, to accompany future studies on CPA toxicity. Four common CPAs, namely, dimethyl sulfoxide, ethylene glycol, propylene glycol, and formamide were investigated at various concentrations in aqueous mixtures and compared to pure water. The acoustic spectra of each CPA show an observable dependence on concentration levels and provide a potential way to probe the hydrogen bonding dynamics within the mixtures. [This is a SAWIAGOS project.]

The Applied Research Laboratories has an extensive history of supporting underwater acoustic research through the development of novel high-amplitude underwater sound sources, such as the Plasma Sound Source (PSS), the Combustive Sound Source (CSS) and the Rupture Induced Underwater Sound Source (RIUSS). These sources generate broadband acoustic pulses capable of long-range propagation and seabed penetration, and can be viewed as alternatives to explosive sources. The PSS is based on the discharge of electrical energy stored in capacitors which results in a plasma bubble. The CSS consists of a submersible combustion chamber, open to the water, which is filled with a combustive mixture that is ignited via spark. Upon ignition, the combustive mixture is converted into high temperature combustion byproducts which expand and ultimately collapse, thereby radiating an acoustic pulse. In this talk, the motivation for alternative impulsive sources is discussed and the PSS is briefly discussed. Next, the early development of CSS, through the end of the 1990’s, is described, which led to the basic understanding of the CSS and the parameters required to modify its output. In the following talk further development of CSS, and the invention of RIUSS, are discussed. [Work supported by ONR and NAVO.]

The acoustic coring system (ACS) is a probe-equipped gravity corer that provides in situ measurements of compressional and shear wave speed and attenuation. During an April 2022 coring survey, the ACS was deployed at 36 locations within the New England Mud Patch and New England Shelf Break areas. Data from these measurements will be presented to characterize the depth-dependent structure of the geoacoustic seabed properties as well as their spatial variability. The in situ measurements will be interpreted in the context of stratigraphic layering measured by a seismic survey. Historically, in situ shear speed measurements of the seabed have proved difficult to obtain. From the 2022 survey, depth-dependent (up to 4 meters) shear speed profiles at 800 and 1200 Hz were produced from a subset of the 36 deployments. These results, along with methods for analysis, challenges in the measurements, and supplemental laboratory experiments will be discussed. The results will also be compared to measurements from previous experiments. [Work sponsored by ONR.]

BACKGROUND: Noise exposure in the neonatal intensive care unit (NICU) is consistently higher than current recommendations. This may adversely affect neonatal sleep, weight gain, and overall health. We sought to evaluate the effect of a novel active noise control (ANC) system. METHODS: An ANC device's noise reduction performance was compared to that of adhesively affixed foam ear covers in response to alarm and voice sounds in a simulated NICU environment. The zone of noise reduction of the ANC device was quantified with the same set of alarm and voice sounds. RESULTS: The ANC device provided greater noise reduction than the ear covers in seven of the eight sound sequences tested in which a noise reduction greater than the just noticeable difference was achieved. For noise in the 500 Hz octave band, the ANC device exhibited consistent noise reduction throughout expected patient positions. It provided better performance for noise below 1000 Hz than above 1000 Hz. CONCLUSIONS: The ANC device provided generally superior noise reduction to the ear covers and provided a zone of noise reduction throughout the range where an infant would be placed within an incubator. Implications for patient sleep and weight gain are discussed. IMPACT: Active noise control device can effectively reduce noise inside an infant incubator due to bedside device alarms. This is the first analysis of an incubator-based active noise control device and comparison to adhesively affixed silicone ear covers. A non-contact noise reduction device may be an appropriate means of reducing noise exposure of the hospitalized preterm infant.

Pentamodal (PM) metamaterials are elastic structures that are designed to support purely longitudinal acoustic wave propagation over a wide band of frequencies. Further, these metamaterials can be designed to have anisotropic stiffness and be impedance matched to water [doi.org/10.1121/10.0009161]. Due to the complexity of three-dimensional (3D) PM microstructures, metal additive manufacturing techniques must be employed to physically realize these materials to achieve the specifically tailored impedance and anisotropic sound speeds over the desired frequency range. Previous work designed and built an additively manufactured titanium PM material measuring 98.9x 98.7x87.2 mm3 which was successfully characterized in a fresh-water tank. The current work presents vibration transmissibility measurements on the same PM sample. The structure was mounted on an electro-dynamic shaker which provided a broadband base excitation. Base acceleration and out-of-plane surface accelerations of each exposed face were then measured using point accelerometers and a scanning laser Doppler vibrometer, respectively, and the process was repeated for multiple sample orientations. The observed vibrational modes demonstrate the influence of geometric asymmetry introduced by the truncated domain of the PM lattice. Measurements were compared to a fully-featured finite element model of the sample using COMSOL Multiphysics showing good agreement in mode shapes. [Work supported by ONR]

During Seabed Characterization Experiment 2017 in the New England Mudpatch under near isospeed conditions of the water column, observations were made of well-defined intensity striations in time-frequency spectrograms in the 1.5–4.0 kHz band. These observations provided the basis for the hypothesis that the compressional sound speed profile for a homogenous fine-grained sediment possessed a gradient in the upper portions of the seabed. This hypothesis was tested with a statistical inference method that extracts probability density functions for parameter values representing an empirical-based nonlinear profile whose origins go back to Hamilton. Inferred was a surface sound speed that is less than the sound speed of the water at the seafloor and a surface sound speed gradient of about 6 1/s. In 2022 the experiment was repeated during non-isospeed conditions of the water column. The results for 2017 and 2022 are compared with the intent of understanding the response of the geoacoustic properties of the upper portions of a fine-grained sediment to changes in the bottom water temperature and salinity of the water column. [Work supported by Office of Naval Research.]

Acoustic propagation measurements were collected in a seagrass meadow in a shallow lagoon for periods of over 65 h in winter and 93 h in summer. A bottom-deployed sound source transmitted chirps (0.1-100 kHz) every 10 min that were received on a four-receiver horizontal hydrophone array. Oceanographic probes measured various environmental parameters. Daytime broadband acoustic attenuation was 2.4 dB greater in summer than winter, and the median received acoustic energy levels were 8.4 dB lower in summer compared to winter. These differences were attributed in part to seasonal changes in photosynthesis bubble production and above-ground seagrass biomass.

Seagrasses play an important role in coastal ecosystems and serve as important marine carbon stores. Acoustic monitoring techniques exploit the sensitivity of underwater sound to bubbles, which are produced as a byproduct of photosynthesis and present within the seagrass tissue. To make accurate assessments of seagrass biomass and productivity, a model is needed to describe acoustic propagation through the seagrass meadow that includes the effects of gas contained within the seagrass leaves. For this purpose, a new seagrass leaf model is described for Thalassia testudinum that consists of a comparatively rigid epidermis that composes the outer shell of the leaf and comparatively compliant aerenchyma that surrounds the gas channels on the interior of the leaf. With the bulk modulus and density of the seagrass tissue determined by previous work, this study focused on characterizing the shear moduli of the epidermis and aerenchyma. These properties were determined through a combination of dynamic mechanical analysis and acoustic resonator measurements coupled with microscopic imagery and finite element modeling. The shear moduli varied as a function of length along the leaves with values of 100 and 1.8 MPa at the basal end and 900 and 3.7 MPa at the apical end for the epidermis and aerenchyma, respectively.