Effects of unattended speech on performance and subjective distraction: The role of acoustic design in open-plan offices

Unattended background speech is a known source of cognitive and subjective distraction in open-plan offices. This study investigated whether the deleterious effects of background speech can be affected by room acoustic design that decreases speech intelligibility, as measured by the Speech Transmission Index (STI). The experiment was conducted in an open-plan office laboratory (84 m²) in which four acoustic conditions were physically built. Three conditions contained background speech. A quiet condition was included for comparison. The speech conditions differed in terms of the degree of absorption, screen height, desk isolation, and the level of masking sound. The speech sounds simulated an environment where phone conversations are heard from different locations varying in distance. Ninety-eight volunteers were tested. The presence of background speech had detrimental effects on the subjective perceptions of noise effects and on cognitive performance in short-term memory and working memory tasks. These effects were not attenuated nor amplified within a three-hour working period. The reduction of the STI by room acoustic means decreased subjective disturbance, whereas the effects on cognitive performance were somewhat smaller than expected. The effects of room acoustic design on subjective distraction were stronger among noise-sensitive subjects, suggesting that they benefited more from acoustic improvements than non-sensitive subjects. The results imply that reducing the STI is beneficial for performance and acoustic satisfaction especially regarding speech coming from more distant desks. However, acoustic design does not sufficiently decrease the distraction caused by speech from adjacent desks.     

Logatom corpus for the assessment of the intelligibility in Spanish speaking environments and its relation with STI measurements

A 1000 consonant–vowel–consonant structure logatoms corpus (CVC-structure), grouped in 10 phonetically equally balanced lists of 100 words each, was developed to satisfy the need of subjective assessment of speech intelligibility in American Spanish speaking environments. This corpus was tested and correlated with the Speech Transmission Index (STI) measurements to compare its articulation intelligibility score with other lists’ scores.Through the development of this work it was determined that in two different acoustically poor rooms that have the same STI (with STI < 0.50), the intelligibility score is lower when the articulation test is performed in a quiet room with high reverberation time than when it is performed in a very noisy room with low reverberation time. The final correlation curve of the American Spanish CVC-structure corpus was around 10% points higher than the CVC_EQB curve obtained by Steeneken and Houtgast in 2002.     

Effect of acoustic frequency and power density on the aqueous ultrasonic-assisted extraction of grape pomace (Vitis vinifera L.) – A response surface approach

Aqueous ultrasound-assisted extraction (UAE) of grape pomace was investigated by Response Surface Methodology (RSM) to evaluate the effect of acoustic frequency (40, 80, 120 kHz), ultrasonic power density (50, 100, 150 W/L) and extraction time (5, 15, 25 min) on total phenolics, total flavonols and antioxidant capacity. All the process variables showed a significant effect on the aqueous UAE of grape pomace (p < 0.05). The Box–Behnken Design (BBD) generated satisfactory mathematical models which accurately explain the behavior of the system; allowing to predict both the extraction yield of phenolic and flavonol compounds, and also the antioxidant capacity of the grape pomace extracts. The optimal UAE conditions for all response factors were a frequency of 40 kHz, a power density of 150 W/L and 25 min of extraction time. Under these conditions, the aqueous UAE would achieve a maximum of 32.31 mg GA/100 g fw for total phenolics and 2.04 mg quercetin/100 g fw for total flavonols. Regarding the antioxidant capacity, the maximum predicted values were 53.47 and 43.66 mg Trolox/100 g fw for CUPRAC and FRAP assays, respectively. When comparing with organic UAE, in the present research, from 12% to 38% of total phenolic bibliographic values were obtained, but using only water as the extraction solvent, and applying lower temperatures and shorter extraction times. To the best of the authors’ knowledge, no studies specifically addressing the optimization of both acoustic frequency and power density during aqueous-UAE of plant materials have been previously published.     

Aircraft noise-monitoring according to ISO 20906: Evaluation of uncertainty derived from the human factors affecting event detection

One of the most important issues in aircraft noise monitoring systems is the correct detection and marking of aircraft sound events through their measurement profiles, as this influences the reported results. In the recent ISO 20906 (unattended monitoring of aircraft sound in the vicinity of airports) this marking task is split into: detection from the sound level time history, classification of probable aircraft sound events, and the concluding identification of aircraft sound events through non-acoustic features.An experiment was designed to evaluate the factors that influence the marking tasks and quantify their contribution to the uncertainty of the reported monitoring results for some specific cases. Several noise time histories, recorded in three different locations affected by flyover noise, were analyzed by practitioners selected according to three different expertise levels. The analysis was carried out considering three types of complementary information: noise recordings, list of aircraft events and no information at all.Five European universities and over 60 participants were involved in this experiment.The results showed that there were no significant differences in the results derived from factors such as the participant’s institution or the expertise of the practitioners. Nonetheless, other factors, like the noise event dynamic range or the type of help used for marking, have a statistically significant influence on the marking tasks. They cause an increase of the uncertainty of the reported monitoring and can lead to changes in the overall results.The experiment showed that, even when there are no classification and identification errors, the detection stage causes uncertainty in the results. The standard uncertainty for detection ranges from 0.3 dB for those acoustic environments where aircraft are clearly detectable to almost 2 dB in more difficult environments.     

Influence of coding strategies in electric-acoustic hearing: A simulation dedicated to EAS cochlear implant,in the presence of noise

This work deals with electric-acoustic stimulation (EAS), which keeps the low frequency acoustic information and electrically codes the high frequencies of the signal. One of the goals of the coding strategies is to limit the phenomenon of channel interaction, which can occur in CIs. The “N-of-M” strategy, where only a subset of electrode channels is stimulated, may be of advantage. Generally, this processing is associated with a pre-emphasis filter. Two important parameters for the N-of-M strategy are the number of active channels (N) and the updating rate; the latter corresponds to the stimulation rate. M is the number of electrical channels.The goal of this study was to investigate the influence of these parameters on speech intelligibility in EAS. The signal was presented, in simulation, to normal-hearing (NH) subjects in acoustic (A), electric (E) and electric-acoustic conditions. Recognition performance was measured in quiet and in the presence of background noise (cafeteria noise).Signal-to-noise ratios (SNRs) ranged from 0 to +12 dB. Fifteen listeners participated in the experiment. The N values ranged from 2 to 10 (out of 10); M was 10. The frame updating rate was 250 updates per second (ups) and 1000 ups.Results showed that increasing N from 2 to 10 improved speech intelligibility, especially in the presence of the background noise, under E and EAS conditions. In noisy situations, 2/10 coupled with a high-pass pre-emphasis filter led to results similar to the 10/10 condition. Changing the frame rate from 250 ups to 1000 ups did not modify the performance.Future investigations on patients using EAS are now needed to validate the performance seen with NH listeners. Above all, in the strategy 2 out of 10, the number of pulses per second can be divided by 20, and when the pre-emphasis is used only a slight decrease in performance is expected; this is of interest when interaction between the electrodes corrupts the performance.     

Intensification of ultrasonic-assisted crude oil demulsification based on acoustic field distribution data

Water removal is an essential step during crude oil production due to several problems such as increased transportation costs and high corrosion rate due to dissolved salts. Indirect low frequency ultrasonic energy (US), using baths, has been recently proposed as an effective alternative for crude oil demulsification. However, the reactor position during sonication and its influence on the demulsification efficiency for crude oil has not been evaluated. In this sense, the aim of this study was to develop an automated system based on an open source hardware for mapping the acoustic field distribution in an US bath operating at 35 kHz using a hydrophone. Data acquired with this system provided information to evaluate the demulsification efficiency in the different positions of the US bath and correlate it with the acoustic intensity distribution. The automated 3D-mapping system revealed a higher acoustic intensity in the regions immediately above the transducers (ca. 0.6 W cm⁻²), while the other regions presented a relatively lower intensity (ca. 0.1 W cm⁻²). Experimental data demonstrated that reactors positioned in the most intense acoustic regions provided a much higher efficiency of demulsification in comparison with the ones positioned in the less intense acoustic field regions. Demulsification efficiency up to 93% was obtained with 15 min of sonication (100% amplitude) using few amount of chemical demulsifier. Hence, this work demonstrated that the information acquired with the developed mapping system could be used for inducing a higher efficiency of demulsification only by finding the more suitable position of reactor in the US bath, which certainly will help development of appropriate reactors design when looking for such approach.     

Combining COMSOL modeling with acoustic pressure maps to design sono-reactors

Scaled-up and economically viable sonochemical systems are critical for increased use of ultrasound in environmental and chemical processing applications. In this study, computational simulations and acoustic pressure maps were used to design a larger-scale sono-reactor containing a multi-stepped ultrasonic horn. Simulations in COMSOL Multiphysics showed ultrasonic waves emitted from the horn neck and tip, generating multiple regions of high acoustic pressure. The volume of these regions surrounding the horn neck were larger compared with those below the horn tip. The simulated acoustic field was verified by acoustic pressure contour maps generated from hydrophone measurements in a plexiglass box filled with water. These acoustic pressure contour maps revealed an asymmetric and discrete distribution of acoustic pressure due to acoustic cavitation, wave interaction, and water movement by ultrasonic irradiation. The acoustic pressure contour maps were consistent with simulation results in terms of the effective scale of cavitation zones (∼10 cm and <5 cm above and below horn tip, respectively). With the mapped acoustic field and identified cavitation location, a cylindrically-shaped sono-reactor with a conical bottom was designed to evaluate the treatment capacity (∼5 L) for the multi-stepped horn using COMSOL simulations. In this study, verification of simulation results with experiments demonstrates that coupling of COMSOL simulations with hydrophone measurements is a simple, effective and reliable scientific method to evaluate reactor designs of ultrasonic systems.     

Enhancement of cavitation activity and particle removal with pulsed high frequency ultrasound and supersaturation

Megasonic cleaning as applied in leading edge semiconductor device manufacturing strongly relies on the phenomenon of acoustic cavitation. As the occurrence of acoustic cavitation is incorporating a multitude of interdependent effects, the amount of cavitation activity in the cleaning liquid strongly depends on the sonication conditions. It is shown that cavitation activity as measured by means of ultraharmonic cavitation noise can be significantly enhanced when pulsed sonication is applied to a gas supersaturated liquid under traveling wave conditions. It is demonstrated that this enhancement coincides with a dramatic increase in particle removal and is therefore of great interest for megasonic cleaning applications. It is demonstrated that the optimal pulse parameters are determined by the dissolution time of the active bubbles, whereas the amount of cavitation activity depends on the ratio between pulse-off and pulse-on time as well as the applied acoustic power. The optimal pulse-off time is independent of the corresponding pulse-on time but increases significantly with increasing gas concentration. We show that on the other hand, supersaturation is needed to enable acoustic cavitation at aforementioned conditions, but has to be kept below values, for which active bubbles cannot dissolve anymore and are therefore lost during subsequent pulses. For the applicable range of gas contents between 100% and 130% saturation, the optimal pulse-off time reaches values between 150 and 340 ms, respectively. Full particle removal of 78 nm-diameter silica particles at a power density of 0.67 W/cm² is obtained for the optimal pulse-off times. The optimal pulse-off time values are derived from the dissolution time of bubbles with a radius of 3.3 μm and verified experimentally. The bubble radius used in the calculations corresponds to the linear resonance size in a 928 kHz sound field, which demonstrates that the recycling of active bubbles is the main enhancement mechanism. The optimal choice of the pulsing conditions however is constrained by the trade-off between the effective sonication time and the desire to have a sufficient amount of active bubbles at lower powers, which might be necessary if very delicate structures have to be cleaned.     

Procedure for verification of sound source coverage over façades according to the International Standard ISO 140–5

This paper presents a new verification procedure for sound source coverage according to ISO 140–5 requirements. The ISO 140–5 standard applies to the measurement of façade insulation and requires a sound source able to achieve a sufficiently uniform sound field in free field conditions on the façade under study. The proposed method involves the electroacoustic characterisation of the sound source in laboratory free field conditions (anechoic room) and the subsequent prediction by computer simulation of the sound free field radiated on a rectangular surface equal in size to the façade being measured. The loudspeaker is characterised in an anechoic room under laboratory controlled conditions, carefully measuring directivity, and then a computer model is designed to calculate the acoustic free field coverage for different loudspeaker positions and façade sizes. For each sound source position, the method provides the maximum direct acoustic level differences on a façade specimen and therefore determines whether the loudspeaker verifies the maximum allowed level difference of 5 dB (or 10 dB for façade dimensions greater than 5 m) required by the ISO standard. Additionally, the maximum horizontal dimension of the façade meeting the standard is calculated and provided for each sound source position, both with the 5 dB and 10 dB criteria. In the last section of the paper, the proposed procedure is compared with another method used by the authors in the past to achieve the same purpose: in situ outdoor measurements attempting to recreate free field conditions. From this comparison, it is concluded that the proposed method is able to reproduce the actual measurements with high accuracy, for example, the ground reflection effect, at least at low frequencies, which is difficult to avoid in the outdoor measurement method, and it is fully eliminated with the proposed method to achieve the free field requisite.     

A miniaturized prototype of resonant banana-shaped photoacoustic cell for gas sensing

A resonant photoacoustic cell intended for laser-spectroscopy gas sensing is represented. This cell is a miniature imitation of a macro-scale banana-shaped cell developed previously. The parameters, which specify the cavity shape, are chosen so as not only to provide optimal cell operation at a selected acoustic resonance but also to reduce substantially the cell sizes. A miniaturized prototype cell (the volume of acoustic cavity of ∼5 mm³) adapted to the narrow diffraction-limited beam of near-infrared laser is produced and examined experimentally. The noise-associated measurement error and laser-initiated signals are studied as functions of modulation frequency. The background signal and the useful response to light absorption by the gas are analyzed in measurements of absorption for ammonia in nitrogen flow with the help of a pigtailed DFB laser diode oscillated near a wavelength of 1.53 μm. The performance of prototype operation at the second longitudinal acoustic resonance (the resonance frequency of ∼32.9 kHz, Q-factor of ∼16.3) is estimated. The noise-limited minimal detectable absorption normalized to laser-beam power and detection bandwidth is ∼8.07 × 10⁻⁸ cm⁻¹ W Hz^−1/2. The amplitude of the background signal is equivalent to an absorption coefficient of ∼2.51 × 10⁻⁵ cm⁻¹. Advantages and drawbacks of the cell prototype are discussed. Despite low absorption-sensing performance, the produced miniaturized cell prototype shows a good capability of gas-leak detection.     

The role of torsional modes in the electronic absorption spectrum of acetone

The electronic absorption spectrum of acetone is revisited to evaluate the role of hot bands due to low lying torsional modes in the assignment of vibronic transitions. The UV–VUV photoabsorption spectrum of acetone is recorded in the energy region 3.5–11.8 eV at a resolution of ～4 meV at 4 eV and ～10 meV at 10 eV using synchrotron radiation. The absorption spectrum is dominated by richly structured Rydberg series (ns, np and nd) converging to the first ionization potential of acetone at 9.708 eV. Careful consideration of hot band contributions from torsional modes and symmetry selection rules have resulted in an improved set of vibronic assignments as compared to earlier room temperature work. Revised quantum defect values for some of the Rydberg transitions and a few new assignments in the nd series are also reported in this paper.     

Ultrasonic extraction of steroidal alkaloids from potato peel waste

Potato processors produce large volumes of waste in the form of potato peel which is either discarded or sold at a low price. Potato peel waste is a potential source of steroidal alkaloids which are biologically active secondary metabolites which could serve as precursors to agents with apoptotic, chemopreventive and anti-inflammatory properties. The present study investigated the relative efficacy of ultrasound assisted extraction (UAE) and solid liquid extraction (SLE) both using methanol, to extract steroidal alkaloids from potato peel waste and identified optimal conditions for UAE of α-solanine, α-chaconine, solanidine and demissidine. Using response surface methodology optimal UAE conditions were identified as an amplitude of 61 μm and an extraction time of 17 min which resulted the recovery of 1102 μg steroidal alkaloids/g dried potato peel (DPP). In contrast, SLE yielded 710.51 glycoalkaloid μg/g DPP. Recoveries of individual glycoalkoids using UAE yielded 273, 542.7, 231 and 55.3 μg/g DPP for α-solanine, α-chaconine, solanidine and demissidine respectively. Whereas for SLE yields were 180.3, 337.6, 160.2 and 32.4 μg/g DPP for α-solanine, α-chaconine, solanidine and demissidine respectively. The predicted values from the developed second order quadratic polynomial equation were in close agreement with the experimental values with low average mean deviation (E < 5%) values. Predicted models were highly significant (p < 0.05) for all parameters studied. This study indicates that UAE has strong potential as an extraction method for steroidal alkaloids from potato peel waste.     

Intensification of heterogeneously catalyzed Suzuki-Miyaura cross-coupling reaction using ultrasound: Understanding effect of operating parameters

Palladium-catalyzed Suzuki-Miyaura cross-coupling reaction is a significant reaction for obtaining industrially important products. The current research work deals with intensification of reaction of 4-bromoanisole and phenylboronic acid catalyzed with 5 wt% Pd/C (5% by weight Pd supported on C available as commercial catalyst) using ultrasound and more importantly, without use of any additional phase transfer catalyst. Heterogeneous catalyst has been selected in the present work so as to harness the benefits of easy separation and the possible limitations of heterogeneous operation are minimized by introducing ultrasonic irradiations. The effect of operating parameters such as ultrasound power, temperature, catalyst loading and molar ratio on the progress of reaction has been investigated. It has been observed that an optimum power, temperature and catalyst loading exist for maximum benefits whereas higher molar ratio was found to be favourable for the progress of the reaction. Also, the use of ultrasound reduced the reaction time from 70 min required in conventional approach to only 35 min under conditions of frequency of 22 kHz, power dissipation of 40 W and catalyst loading as 1.5 mol% (refers to total quantum of catalyst used in the work) in ethanol-water system under ambient conditions. The work also demonstrated successful results at ten times higher volume as compared to the normally used volumes in the case of simple ultrasonic horn. Overall, the work has successfully demonstrated process intensification benefits obtained due to the use of ultrasound for heterogeneously catalyzed Suzuki-Miyaura cross-coupling reaction.     

Comparison of characterization methods in high frequency sonochemical reactors of differing configurations

The aim of this study was to compare different characterization methods in order to evaluate the sonochemical efficiency of a cavitational reactor. The selected characterization methods were calorimetry and dosimetry based on potassium iodide oxidation or nitrite and nitrate ion formation. The effects of experimental parameters on physical and chemical effects of ultrasound were quantified with two transducers at a frequency of 366 kHz. The studied factors comprised temperature (16–28 °C), acoustic power (6–38 W), power density (4–61 W L^?1) and reactor configuration (D_{reactor 1} = 65 mm, D_{reactor 2} = 102 mm). Spectrophotometry was compared to ionic chromatography as a method to quantify nitrite and nitrate ions. Spectrometry was shown to be as representative as ionic chromatography. The reaction system based on the formation of both nitrite and nitrate ions was demonstrated to be as reliable as a potassium iodide dosimeter. The representativity of calorimetry was limited since part of acoustic energy was assumed to be used in the chemical reactions observed by dosimetry. Similar sonochemical efficiencies resulted from an increase of sonified surface (D_{reactor 1} = 65 mm vs. D_{reactor 2} = 102 mm) coupled to a 2-time decrease in power density at a constant emitting surface. The effect of emitting-to-sonified surface area ratio on the acoustic field was apparently limited by the height of the liquid.     

Influence of loudspeaker directivity and measurement geometry on direct acoustic levels over façades for acoustic insulation tests with the International Standard ISO 140-5

The International Standard ISO 140-5 on field measurements of airborne sound insulation of façades establishes that the directivity of the measurement loudspeaker should be such that the variation in the local direct sound pressure level (ΔSPL) on the sample is ΔSPL < 5 dB (or ΔSPL < 10 dB for large façades). This condition is usually not very easy to accomplish nor is it easy to verify whether the loudspeaker produces such a uniform level. Direct sound pressure levels on the ISO standard façade essentially depend on the distance and directivity of the loudspeaker used. This paper presents a comprehensive analysis of the test geometry for measuring sound insulation and explains how the loudspeaker directivity, combined with distance, affects the acoustic level distribution on the façade.The first sections of the paper are focused on analysing the measurement geometry and its influence on the direct acoustic level variations on the façade. The most favourable and least favourable positions to minimise these direct acoustic level differences are found, and the angles covered by the façade in the reference system of the loudspeaker are also determined. Then, the maximum dimensions of the façade that meet the conditions of the ISO 140-5 standard are obtained for the ideal omnidirectional sound source and the piston radiating in an infinite baffle, which is chosen as the typical radiation pattern for loudspeakers.Finally, a complete study of the behaviour of different loudspeaker radiation models (such as those usually utilised in the ISO 140-5 measurements) is performed, comparing their radiation maps on the façade for searching their maximum dimensions and the most appropriate radiation configurations.     

Nonlinear parameter estimation in water-saturated sandy sediment with difference frequency acoustic wave

Difference frequency acoustic wave from nonlinear interaction of two primary acoustic waves at frequencies of 76 and 114 kHz was utilized with a parametric acoustic array theory to estimate the nonlinearity parameter of water-saturated sandy sediment. Such nonlinearity parameter can be used as background information for the nonlinear acoustic investigation of bottom or sub-bottom profiling in the ocean sandy sediments. Because of its lower attenuation the difference frequency acoustic wave method can be usefully applied to estimate the nonlinearity parameter of ocean sediment in the ocean as well as under laboratory conditions. The nonlinearity parameter β for the water-saturated sandy sediment used as a reference in this study was estimated as β = 80.5 ± 5.1 at the difference frequency of 38 kHz. It was agreed very well with that estimated at the difference frequency of 67 kHz, when two primary frequencies were 137 and 204 kHz. The estimated nonlinearity parameter of water-saturated sandy sediment in this study was also compared and analyzed with those estimated in previously published literatures. It was suggested that the difference frequency wave method used to estimate the nonlinearity parameter of water-saturated sandy sediment can be employed as a good method to estimate the nonlinearity parameters of fluid-like granular media.     

Effect of ultrasonic treatment on total phenolic extraction from Lavandula pubescens and its application in palm olein oil industry

The aims of the current study were to evaluate the best technique for total phenolic extraction from Lavandula pubescens (Lp) and its application in vegetable oil industries as alternatives of synthetic food additives (TBHQ and BHT). To achieve these aims, three techniques of extraction were used: ultrasonic-microwave (40 kHz, 50 W, microwave power 480 W, 5 min), ultrasonic-homogenizer (20 kHz, 150 W, 5 min) and conventional maceration as a control. By using the Folin–Ciocalteu method, the total phenolic contents (TPC) (mg gallic acid equivalent/g dry matter) were found to be 253.87, 216.96 and 203.41 for ultrasonic-microwave extract, ultrasonic-homogenizer extract and maceration extract, respectively. The ultrasonic-microwave extract achieved the higher scavenger effect of DPPH (90.53%) with EC₅₀ (19.54 μg/mL), and higher inhibition of β-carotene/linoleate emulsion deterioration (94.44%) with IC₅₀ (30.62 μg/mL). The activity of the ultrasonic-microwave treatment could prolong the induction period (18.82 h) and oxidative stability index (1.67) of fresh refined, bleached and deodorized palm olein oil (RBDPOo) according to Rancimat assay. There was an important synergist effect between citric acid and Lp extracts in improving the oxidative stability of fresh RBDPOo. The results of this work also showed that the ultrasonic-microwave assisted extract was the most effective against Gram-positive and Gram-negative strains that were assessed in this study. The uses of ultrasonic-microwave could induce the acoustic cavitation and rupture of plant cells, and this facilitates the flow of solvent into the plant cells and enhances the desorption from the matrix of solid samples, and thus would enhance the efficiency of extraction based on cavitation phenomenon.     

Sound field of typical single-bed hospital wards

The aim of this paper is to investigate the basic characteristics of sound fields in the increasingly concerned single-bed hospital wards, the effects of commonly used furniture, and the feasibility and strategic use of acoustic simulation techniques for such spaces. Two typical single-bed wards at a Critical Care Unit were selected as the case study site. Eight different room acoustic conditions were created by gradually moving pieces of furniture out of the ward. It has been shown that in the ward without acoustic ceiling, under empty room condition the RT ranged from 0.8 s, typically at low frequency, to 2.3 s at 630 Hz; the variations in both SPL and RT at different receivers were insignificant except at low frequencies, so that in such single-bed wards a diffuse field could be assumed; and longer RT and higher SPL were found when furniture was gradually moved out of the ward. In the ward with acoustic ceiling, the effect of furniture was less. There was a good agreement between measured and simulated RT and SPL, showing the usefulness of computer simulation for this kind of spaces. In the simulation, the effect of surface diffusion coefficient was generally insignificant, whereas the effect of edge diffusion should be taken into account, especially for the RT prediction. The feasibility of geometric simplification was also demonstrated.     

A fully discrete Galerkin method for high frequency exterior acoustic scattering in three dimensions

Standard Galerkin discretization techniques (with locally- or globally-supported basis functions) for boundary integral equations are inefficient for high frequency three dimensional exterior scattering simulations because they require a fixed number of unknowns per wavelength in each dimension, leading to large CPU time and memory requirements to set up the dense Galerkin matrix, with each entry requiring evaluation of multi-dimensional highly oscillatory integrals. In this work, using globally-supported basis functions, we describe an efficient fully discrete Galerkin surface integral equation algorithm for simulating high frequency acoustic scattering by three dimensional convex obstacles that includes a powerful integration scheme for evaluation of four dimensional Galerkin integrals with high-order accuracy. Such high-order order accuracy for various practically relevant frequencies (k ∈ [1, 100,000]) substantially improves on approximations based on standard asymptotic techniques. We demonstrate the efficiency of our algorithm for spherical and non-spherical convex scattering for several wavenumbers 1 ? k ? 100,000 for low to high order prescribed tolerance. Our fully discrete algorithm requires only mild growth in the number of unknowns and CPU time as the frequency increases.     

Mechanical bioeffects of acoustic droplet vaporization in vessel-mimicking phantoms

This study investigated the mechanical bioeffects exerted by acoustic droplet vaporization (ADV) under different experimental conditions using vessel phantoms with a 200-μm inner diameter but different stiffness for imitating the microvasculature in various tumors. High-speed microscopy, passive cavitation detection, and ultrasound attenuation measurement were conducted to determine the morphological characteristics of vascular damage and clarify the mechanisms by which the damage was initiated and developed. The results show that phantom erosion was initiated under successive ultrasound exposure (2 MHz, 3 cycles) at above 8-MPa peak negative pressures (PNPs) when ADV occurred with inertial cavitation (IC), producing lesions whose morphological characteristics were dependent on the amount of vaporized droplets. Slight injury occurred at droplet concentrations below (2.6 ± 0.2) × 10⁶ droplets/mL, forming shallow and rugged surfaces on both sides of the vessel walls. Increasing the droplet concentration to up to (2.6 ± 0.2) × 10⁷ droplets/mL gradually suppressed the damage on the distal wall, and turned the rugged surface on the proximal wall into tunnels rapidly elongating in the direction opposite to ultrasound propagation. Increasing the PNP did not increase the maximum tunnel depth after the ADV efficiency reached a plateau (about 71.6 ± 2.7% at 10 MPa). Increasing the pulse duration effectively increased the maximum tunnel depth to more than 10 times the diameter of the vessel even though there was no marked enhancement in IC dose. It can be inferred that substantial bubble generation in single ADV events may simultaneously distort the acoustic pressure distribution. The backward ultrasound reinforcement and forward ultrasound shielding relative to the direction of wave propagation augment the propensity of backward erosion. The results of the present work provide information that is valuable for the prevention or utilization of ADV-mediated mechanical bioeffects in clinical applications.