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The complex acoustic intensity method is one of the common methods used for the azimuth estimation of single-vector sensors. However, this method establishes a relationship between frequency and azimuth, which limits its practical applicability for multiple linear frequency modulation (LFM) signals with overlapping frequency domains. In this paper, the time–frequency distribution information of the LFM signal is combined with the complex acoustic intensity method, and more signal parameter information is used to expand the application scenario of the single-vector sensor. The proposed method first processes the time–frequency graph of the signal to obtain a stable and clear time–frequency distribution, and then obtains the acoustic intensity distribution of the signal using the time integration of the energy on the ridge of the signal to estimate the target orientation more stably. The simulation results show that the root mean square error of azimuth estimation is less than 1° when the SNR is greater than 0 dB. Furthermore, a pool experiment was carried out to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The complex acoustic intensity method is one of the common methods used for the azimuth estimation of single-vector sensors. However, this method establishes a relationship between frequency and azimuth, which limits its practical applicability for multiple linear frequency modulation (LFM) signals with overlapping frequency domains. In this paper, the time–frequency distribution information of the LFM signal is combined with the complex acoustic intensity method, and more signal parameter information is used to expand the application scenario of the single-vector sensor. The proposed method first processes the time–frequency graph of the signal to obtain a stable and clear time–frequency distribution, and then obtains the acoustic intensity distribution of the signal using the time integration of the energy on the ridge of the signal to estimate the target orientation more stably. The simulation results show that the root mean square error of azimuth estimation is less than 1° when the SNR is greater than 0 dB. Furthermore, a pool experiment was carried out to verify the effectiveness of the proposed method.

Highlights: [•] The freezing time and quality of broccoli subjected to UAF were studied. [•] Ultrasound acoustic intensity within 0.250–0.412 W/cm2 was optimal for broccoli freezing. [•] UAF decreased the freezing time within 0.250–0.412 W/cm2 acoustic intensity levels. [•] Microstructure, physical and chemical quality of broccoli were better preserved by UAF. [•] Outside that acoustic intensity range, the quality of the frozen broccoli was inferior. [ABSTRACT FROM AUTHOR]

Abstract: With the popularity of ultrasound therapy in clinics, characterization of the acoustic field is important not only to the tolerability and efficiency of ablation, but also for treatment planning. A quantitative method was introduced to assess the intensity distribution of a focused ultrasound beam using a hydrophone and an infrared camera with no prior knowledge of the acoustic and thermal parameters of the absorber or the configuration of the array elements. This method was evaluated in both theoretical simulations and experimental measurements. A three-layer model was developed to calculate the acoustic field in the absorber, the absorbed acoustic energy during the sonication and the consequent temperature elevation. Experiments were carried out to measure the acoustic pressure with the hydrophone and the temperature elevation with the infrared camera. The percentage differences between the derived results and the simulation are <4.1% for on-axis intensity and <21.1% for −6-dB beam width at heating times up to 360 ms in the focal region of three phased-array ultrasound transducers using two different absorbers. The proposed method is an easy, quick and reliable approach to calibrating focused ultrasound transducers with satisfactory accuracy. [Copyright &y& Elsevier]

We show that the experimental data for the action of ultrasonic waves on homeotropically aligned nematic-liquid-crystal cells reported by Kapustina, in Akust. Zh. 54, 900 (2008) [Acoust. Phys. 54, 778 (2008)] can be explained in the framework of the director-density coupling theory in the regime of low acoustic intensity. This result therefore provides support for the hypothesis that the interaction between sound and nematic liquid crystals is dominated by an elastic energy. [ABSTRACT FROM AUTHOR]

Several rain drop size distribution (DSD) point measurement technologies exist, but all are unable to sample either short timescales or the large drop tail of the DSD due to inherent instrumental limitations. The development of an acoustic water tank disdrometer (AWTD) is described, which improves the sampling statistics by increasing the catchment area. This is achieved by distinguishing individual drops, locating them on the surface of the tank then converting the impact pressure into a drop size. Wavelet decomposition is used to distinguish the broadband, short duration impact events and a fast multilateration method is used to position the drop. Issues relating to the different types of noise are also investigated and mitigated. Also, further work on inverting the measured acoustic intensity into a DSD, by fitting sampling distributions, is presented. Six months of data were collected in the Eastern UK. The AWTD then converted the data into DSDs and the results were compared to a commercially available co-located laser precipitation monitor. The sampling errors are far lower due to the increased catchment size, and hence the large drop sized tail of the DSD is greatly improved. DSD results compare favourably to other disdrometers for drop diameters greater than 1.8 mm. Below this size individual drops become increasingly difficult to detect and are underestimated. [ABSTRACT FROM AUTHOR]

Abstract: This work presents a new technique for the computation of the numerical equivalent to the supersonic acoustic intensity, for arbitrarily shaped sound sources. The technique provides therefore the identification of the regions of a noise source that effectively contribute to the sound power radiated into the far field by filtering non-propagating sound waves. The proposed technique is entirely formulated on the vibrating surface. The radiated acoustic power is obtained through a numerical operator that relates it with the superficial normal velocity distribution. The power operator is obtained by using the boundary element method. Such operator, possesses the property of being Hermitian. The advantage of this characteristic is that it has real eigenvalues and their eigenvectors form an orthonormal set for the velocity distribution. It is applied to the power operator the decomposition in eigenvalues and eigenvectors, becoming possible to compute the numerical equivalent to the supersonic intensity, called here as useful intensity, after applying a cutoff criterion to remove the non-propagating components. Some numerical tests confirming the effectiveness of the convergence criterion are presented. Examples of the application of the useful intensity technique in vibrating surfaces such as a plate, a cylinder with flat caps and an automotive muffler are presented and the numerical results are discussed. [Copyright &y& Elsevier]

Our recently developed ultrasound-switchable fluorescence (USF) imaging technique showed that it was feasible to conduct high-resolution fluorescence imaging in a centimeter-deep turbid medium. Because the spatial resolution of this technique highly depends on the ultrasound-induced temperature focal size (UTFS), minimization of UTFS becomes important for further improving the spatial resolution USF technique. In this study, we found that UTFS can be significantly reduced below the diffraction-limited acoustic intensity focal size via nonlinear acoustic effects and thermal confinement by appropriately controlling ultrasound power and exposure time, which can be potentially used for deep-tissue high-resolution imaging. [ABSTRACT FROM AUTHOR]

The acoustic intensity vector field around a tuning fork is investigated. Theory for a longitudinal quadrupole source predicts a well-defined transition between near-field and far-field, with significant circulation of sound energy in the near-field. Vector components of the time-averaged intensity were measured using a two-microphone intensity probe and found to agree well with predictions from theory. The vector intensity map is interpreted, and shown to provide useful information about the near-field of an acoustic source. [ABSTRACT FROM AUTHOR]

Patterns of acoustic intensity profiles are investigated in recorded performances of the music of Haydn. Consistent with our earlier observations of composed, acousmatic, live-performed, and improvised electroacoustic music, and of jazz improvisations (Dean & Bailes, 2010a, b), we hypothesised that in successive pairs of intensity rises and falls, rises are shorter in duration relative to falls, follow a faster rate of dynamic intensity change (decibel change / time), but are not significantly different in frequency of occurrence. We ask here whether this hypothesis is applicable to interpretations of 119 movements of Haydn's works. We consider a wide range of instrumental groupings, from solo to orchestral, and we also consider multiple performances of single pieces. The hypothesised pattern was routinely observed. We also took note of alternative predictions that might flow from the 'ramp archetype' observed by Huron (1991) in notated scores of the classical and romantic era, notably in the scores of the Beethoven piano sonatas and others. This statistical archetype might suggest, contrary to our hypothesis, that performed crescendi are longer in duration than diminuendi, greater in their frequency of occurrence, and follow a more gradual rate of intensity change. Thus we also investigate our hypothesis in relation to a sample of the Beethoven sonatas included in Huron's (1990) score analysis. The data on Beethoven are again consistent with our hypothesis, and we conclude that it is appropriate to these performances also. The observations can be understood in terms of the psychology of expectation and attention, and we discuss the possibility that they apply to vocal and natural sounds, either of which might allow an explanation for their occurrence in music. [ABSTRACT FROM AUTHOR]

Sound visualization techniques have played a key role in the development of acoustics throughout history. The development of measurement apparatus and techniques for displaying sound and vibration phenomena has provided excellent tools for building understanding about specific problems. Traditional methods, such as step-by-step measurements or simultaneous multichannel systems, have a strong tradeoff between time requirements, flexibility, and cost. However, if the sound field can be assumed time stationary, scanning methods allow us to assess variations across space with a single transducer, as long as the position of the sensor is known. The proposed technique, Scan and Paint, is based on the acquisition of sound pressure and particle velocity by manually moving a P-U probe (pressure-particle velocity sensors) across a sound field whilst filming the event with a camera. The sensor position is extracted by applying automatic color tracking to each frame of the recorded video. It is then possible to visualize sound variations across the space in terms of sound pressure, particle velocity, or acoustic intensity. In this paper, not only the theoretical foundations of the method, but also its practical applications are explored such as scanning transfer path analysis, source radiation characterization, operational deflection shapes, virtual phased arrays, material characterization, and acoustic intensity vector field mapping. [ABSTRACT FROM AUTHOR]

Summary: Background: Ultrasound perfusion imaging (UPI) with bolus kinetic has been shown to be feasible at bedside for evaluation of perfusion deficits in stroke patients. Recent technical advances allow perfusion imaging with refill kinetics using a low mechanical index. Methods: We examined 31 acute middle cerebral artery (MCA) stroke patients with transcranial color-coded duplex ultrasound (TCCD) and UPI. The refill of microbubbles was calculated from regions of interest in the ischemic area and the contralateral MCA territory by using the exponential function y = A(1− e βt ); A =acoustic intensity of the plateau (dB), β =slope (1/s). Results: We found significantly lower values of β in the ischemic area compared with the contralateral MCA territory (0.75 vs. 1.051/s, p <0.05); particularly in patients with a pathological MCA flow pattern on TCCD (0.61 vs. 1.01, p <0.01). There was a high interindividual variance without significant difference of the plateau of acoustic intensity (A) in any subgroup of patients. Discussion: The slope parameter β of refill kinetics is useful for assessing brain perfusion in patients with acute stroke and pathological flow pattern of the ipsilateral MCA. The parameter A, however, seems more dependent from the quality of the temporal bone window. [ABSTRACT FROM AUTHOR]

A systematic technique has been developed to determineantiscalingefficiency and dissolution capacity for calcium carbonate in oilfieldbrines under various ultrasonic treating conditions. During the staticexperiments, effects of ultrasonic frequency, acoustic intensity,treating time, and water level on the antiscaling efficiency havebeen evaluated, while the underlying antiscaling mechanism is identifiedand determined. Physically, the formation of calcium carbonate ispromoted as a result of the decreased molecular force and acceleratedmovement of salty ions under ultrasonic irradiation. Most of the formedscale is found to loosely suspend in the liquid, rather than tightlyadhere to the solid surface. During the dynamic experiments, orthogonaltests have been designed to examine effects of interval time, treatingtime, and flow velocity on antiscaling efficiency. As for the dissolutionexperiment, dissolution capacity is measured to evaluate the effectof ultrasonic frequency on dissolution of the formed calcium carbonate.The antiscaling efficiency is found to achieve its maximum value of81.1%, using the ultrasonic treatment with a frequency of 28 kHz,an acoustic intensity of 0.61 W/cm2, an interval time of2 h, a treatment time of 15 min, and a flow velocity of 1.8 m/s. Itis also found that dissolution capacity does not impose a dominanteffect on scale prevention and that the highest dissolution capacityof 19.3% is obtained with an ultrasonic frequency of 28 kHz. [ABSTRACT FROM AUTHOR]

High-frequency mechanical vibrations (20–50 kHz), delivered via small diameter flexible wire waveguides represent a minimally invasive technology for the treatment of chronic total occlusions and in other tissue ablation applications. Tissue disruption is reported to be caused by repetitive mechanical contact and cavitation. This work focuses on the effects of vibrating wire waveguides in contact with arterial tissue. An apparatus with clinically relevant parameters was used, characterized as operating at 22.5 kHz and delivering amplitudes of vibration of 17.8–34.3 μm (acoustic intensity, ISATA: 1.03–3.83 W/cm^2) via 1.0-mm diameter waveguides. Inertial cavitation (in water at 37 °C) was determined to occur above amplitudes of vibration greater than 31.4 μm (ISATA = 3.21 W/cm ^2). The energized waveguides were advanced through tissue samples (porcine aorta) and the force profiles were measured for a range of acoustic intensities. The results show that the tissue perforation initiation force, perforation initiation energy, and total energy required to perforate the tissue reduces with increasing acoustic intensity. No significant reduction in perforation force or energy was observed in the inertial cavitation region. Multistage perforation was evident through the force profile and histological examination of the tissue samples post wire waveguide perforation. [ABSTRACT FROM PUBLISHER]

With the two-choice go/no-go paradigm, we investigated whether timbre attribute can be transmitted as partial information from the stimulus identification stage to the response preparation stage in auditory tone processing. We manipulated two attributes of the stimulus: timbre (piano vs. violin) and acoustic intensity (soft vs. loud) to ensure an earlier processing of timbre than intensity. We associated the timbre attribute more with go trials. Results showed that lateralized readiness potentials ( LRPs) were consistently elicited in no-go trials. This showed that the timbre attribute had been transmitted to the response preparation stage before the intensity attribute was processed in the stimuli identification stage. Such a result provides evidence for the continuous model and asynchronous discrete coding ( ADC) model in information processing. We suggest that partial information can be transmitted in an auditory channel. [ABSTRACT FROM AUTHOR]

Abstract: The seasonal patterns of marine circulation and biovolume were obtained from time-series measurements carried out in the “Parque Nacional Sistema Arrecifal Veracruzano” (PNSAV), located in the western continental shelf of the Gulf of Mexico, from June 2008 to September 2009. Two mechanisms were depicted as the responsible for the current pattern observed in the PNSAV and not only one as suggested in large-scale studies. The first mechanism is the wind generated currents. This mechanism by itself is responsible for up to 78% of total variation of the seasonal circulation in the PNSAV as estimated with the first mode of the EOF’s (Empirical Orthogonal Functions), which was correlated (Normalized Lagged Correlation) with the north-south wind component. Therefore, the wind and the first mode were highly correlated for most of the year (r > 0.7). The second mode was attributed to the low frequency current, associated to the meso-scale circulation of the Gulf of Mexico, owing to the cyclonic eddy of the Campeche Bay. Both mechanisms were mostly observed throughout the year. Nevertheless, the cyclonic eddy of the Campeche Bay (meso-scale) was the first responsible for the current fluctuations observed during the summer of 2008 and 2009. The absolute acoustic intensity (plankton biovolumes) was highly correlated to currents, showing high spatial variability, attributed to advection produced by the meso-scale circulation and to river discharges, but also by eddy diffusion produced by atmospheric and coastal water fronts. [Copyright &y& Elsevier]

Abstract: The purpose of this article is to develop a simple mathematical model to address some bioeffects which may be caused by a static attractive force between two long neighboring parallel thin fibers (for example, a pair of collagen bundles of connective tissue) when they are insonificated by a continuous (CW) traveling plane ultrasound (US) under the condition that the fiber length (L)≫the distance between them (h) and h ≪the wavelength of US (λ). The theory predicts that there is an attractive force between these fibers when they are exposed to the CW US with an intensity of a magnitude of 100mW/cm2. The relationship between the relative approaching velocity of the fibers and the acoustic pressure amplitude can be calculated using the theory. An experiment was performed to verify the theoretical predictions. A plastic test chamber (diameter×height=6mm×3.5mm) with a cap made of a sound-absorbing material and filled full with distilled water was placed on a microscope stage. A polymer fiber pair of 100μm diameter (d) and 4mm length (L) were immersed in water and aligned parallel in a plane which is normal to the US propagation direction. They floated at the central area of the chamber and h ⩽10d. A 25mm diameter, 1MHz quartz crystal was used as an ultrasound source as well as the bottom of the test chamber. The quartz crystal was gold-coated on both sides, but a 5mm diameter center was left transparent (electrode free) to enable optical observation via a microscope. The maximum acoustic intensity, I max, of the CW wave generated by the source was set at 300mW/cm2; the corresponding acoustic pressure amplitude was 100kPa. The magnitude of the average approaching velocity of the fiber pair due to the attractive force was found in agreement with that predicted by the theory. [Copyright &y& Elsevier]

Shock waves were explored in the thermoacoustic spontaneous gas oscillations occurring in a gas column with a steep temperature gradient. The results show that a periodic shock occurs in the traveling wave mode in a looped tube but not in the standing wave mode in a resonator. Measurements of the harmonic components of the acoustic intensity reveal a clear difference between them. The temperature gradient acts as an acoustic energy source for the harmonic components of the shock wave in the traveling wave mode but as an acoustic energy sink of the second harmonic in the standing wave mode. [ABSTRACT FROM AUTHOR]

ASTM E-477 is the current standard test method used in North America for evaluating the acoustic and aerodynamic performance of duct silencers. The test method uses, at a minimum, a source chamber, a test duct (that includes a test specimen), and a reverberation chamber. If testing under flow is desired, the system also requires a fan chamber that can provide quiet airflow through the test duct. The results of the test method yield silencer insertion loss, self-generated noise, both as a function of acoustic frequency and flow velocity, and pressure drop. There are several problems with the current test method, some that are being addressed by the ASTM working group that is responsible for the development and maintenance of this standard. This article highlights the most significant problems associated with the current standard and proposes modifications to the standard that should, if adopted, improve the intralaboratory reproducibility of the test results. [ABSTRACT FROM AUTHOR]

Abstract: Progress in developing a new measurement method for ultrasound output power is described. It is a thermal-based technique with the acoustic power generated by a transducer being absorbed within a specially developed polyurethane rubber material, whose high absorption coefficient ensures energy deposition within a few mm of the ultrasonic wave entering the material. The rate of change of temperature at the absorber surface is monitored using the pyroelectric voltage generated from electrodes disposed either side of a 60mm diameter, 0.061mm thick membrane of the piezoelectric polymer polyvinylidene fluoride (pvdf) bonded to the absorber. The change in the pyroelectric output voltage generated by the sensor when the transducer is switched ON and OFF is proportional to the delivered ultrasound power. The sensitivity of the device is defined as the magnitude of these switch voltages to a unit input stimulus of power (watt). Three important aspects of the performance of the pyroelectric sensor have been studied. Firstly, measurements have revealed that the temperature dependent sensitivity increases over the range from approximately 20°C to 30°C at a rate of +1.6%°C−1. Studies point to the key role that the properties of both the absorbing backing layer and pvdf membrane play in controlling the sensor response. Secondly, the high sensitivity of the technique has been demonstrated using an NPL Pulsed Checksource, a 3.5MHz focused transducer delivering a nominal acoustic power level of 4mW. Finally, proof-of-concept of a new type of acoustic sensor responding to time-averaged intensity has been demonstrated, through fabrication of an absorber-backed hydrophone of nominal active element diameter 0.4mm. A preliminary study using such a device to resolve the spatial distribution of acoustic intensity within plane-piston and focused 3.5MHz acoustic fields has been completed. Derived beam profiles are compared to conventional techniques that depend on deriving intensity from acoustic pressure measurements made using the sensor as a calibrated hydrophone. [Copyright &y& Elsevier]

The properties of the scattered acoustic vector fields generated by simple spheres illuminated by monotonic continuous wave (CW) plane waves are investigated. Analytical solutions are derived from general acoustic pressure scattering models and analyzed for wave numbers in the resonance region. Of particular interest is the understanding of the characteristics of the scattered acoustic vector field in the near-to-far-field transition region. The separable active and reactive components of the acoustic intensity are used to investigate the structural features of the scattered field components. Numerical results are presented for the near and transition regions for a rigid sphere. A method of mapping nulls in the scattered intensity field components is described. The analysis is then extended to include a simple fluid-filled boundary and finally the evacuated thin-walled shell. Near field acoustic intensity field structures are compared against mechanical material properties of vacuous shells. The ability to extract scattered field features is illustrated with measurements obtained from a recent in-air experiment using an anechoic chamber and acoustic vector sensor probes to measure the scattered acoustic vector field from rigid spheres. [ABSTRACT FROM AUTHOR]

Listener perceptions of changes in the arousal expressed by classical music have been found to correlate with changes in sound intensity/loudness over time. This study manipulated the intensity profiles of different pieces of music in order to test the causal nature of this relationship. Listeners (N = 38) continuously rated their perceptions of the arousal expressed by each piece. An extract from Dvorak's Slavonic Dance Opus 46 No 1 was used to create a variant in which the direction of change in intensity was inverted, while other features were retained. Even though it was only intensity that was inverted, perceived arousal was also inverted. The original intensity profile was also superimposed on three new pieces of music. The time variation in the perceived arousal of all pieces was similar to their intensity profile. Time series analyses revealed that intensity variation was a major influence on the arousal perception in all pieces, in spite of their stylistic diversity. [ABSTRACT FROM AUTHOR]

Abstract: Sonodynamic therapy (SDT) has been shown to mediate apoptosis in many experimental systems, but the detailed mechanism of this process is unclear. In this study, we aim to investigate the potential participation of the mitochondria-caspase signaling pathway in the SDT-induced apoptosis in isolated sarcoma 180 (S180) cells. The cell suspension was treated with 1.75MHz continuous ultrasound (US) at an acoustic intensity (I SATA) of 1.4W for 3min in the absence or presence of 20μg/ml hematoporphyrin (Hp). At different times after the SDT-treatment, the apoptotic cells were identified under a scanning electron microscope, and the apoptosis index (AI) was determined by flow cytometry. In addition, the mitochondrial membrane potential, permeabilization of the inner mitochondrial membrane, and translocation of apoptosis-related proteins were assessed by confocal microscopy. Simultaneously, the activation of some special apoptosis-associated proteins [caspase-9, caspase-3, polypeptide poly (ADP-ribose) polymerase (PARP), and Bax] was evaluated by western blotting. Our results indicate that the ultrasonically activated Hp can cause obvious cell apoptosis (AI, 57.66%) at 3h after treatment, and this effect can be significantly reduced by caspase-9 inhibitor (AI, 20.76%) and the oxygen scavenger NaN3 (20.11%). However, the apoptosis induced by ultrasound alone was relatively lower (28.33%) and was not reduced by NaN3. Further, SDT caused an 82.1% reduction in the mitochondrial membrane potential and a 70.7% reduction in the permeabilization of the inner mitochondrial membrane immediately after treatment, and these two effects were obviously prevented by NaN3. In comparison with the control cells, the SDT-treated cells showed obvious cytochrome-c and Bax translocations, caspase activation, Bax expression, and PARP cleavage at 1h after SDT-treatment. However, in the cells treated with ultrasound alone, these phenomena partially and weakly occurred 3h after exposure. These results primarily showed that the mitochondria-caspase signaling pathway in S180 cells was activated in the US- and SDT-induced apoptosis. Moreover, Hp significantly accelerates the process of apoptosis and enhances the cytotoxic effect of ultrasonic treatment. Singlet oxygen may be responsible for the mitochondrial damage and the activation of the apoptotic signaling pathway. [Copyright &y& Elsevier]

A seven-microphone three dimensional (3D) intensity measuring system has been developed and evaluated for performance for a broad frequency band (200 Hz–6.5 kHz). Six microphones are arranged in a concentric array with one microphone at the center of the probe. The screw adjustable center microphone is the probe reference microphone, and is used for calibrations of the other microphones in the probe. This probe addresses limitations of the traditional two-microphone system in measuring acoustical properties in a 3D space from the one dimensional measurements. This probe also eliminates the need of spacers used in the existing 3D probes for broadband measurements. Diffraction and reflection effects on calibrations due to presence of the microphones and the probe supporting structure are negligible. This seven-microphone probe provided better results in the intensity measurements for the wide frequency band than that of a similar four-microphone array probe. [ABSTRACT FROM AUTHOR]

In this study, the Harmonic Motion Imaging for Focused Ultrasound (HMIFU) technique is applied to monitor changes in mechanical properties of tissues during thermal therapy in a transgenic breast cancer mouse model in vivo. An HMIFU system, composed of a 4.5-MHz focused ultrasound (FUS) and a 3.3-MHz phased-array imaging transducer, was mechanically moved to image and ablate the entire tumor. The FUS transducer was driven by an amplitude-modulated (AM) signal at 15 Hz. The acoustic intensity (Ispta) was equal to 1050 W/cm2 at the focus. A digital low-pass filter was used to filter out the spectrum of the FUS beam and its harmonics prior to displacement estimation. The resulting axial displacement was estimated using 1-D cross- correlation on the acquired RF signals. Results from two mice with eight lesions formed in each mouse (16 lesions total) showed that the average peak-to-peak displacement amplitude before and after lesion formation was respectively equal to 17.34 ± 1.34 μm and 10.98 ± 1.82 μm (p < 0.001). Cell death was also confirmed by hematoxylin and eosin histology. HMI displacement can be used to monitor the relative tissue stiffness changes in real time during heating so that the treatment procedure can be performed in a time-efficient manner. The HMIFU system may, therefore, constitute a cost-efficient and reliable alternative for real-time monitoring of thermal ablation. [ABSTRACT FROM AUTHOR]

Abstract: A methodology for assessing the quality and analysing the sound field of a numerical solution for an aeroacoustic problem is presented using an in-duct propagation problem as example. Namely an analysis of the acoustic energy conservation provides insight about the solution quality; sources of numerical error as well as physical source of sound are located by an analysis of the acoustic intensity; a mode analysis provides information about the sound field in the duct and a visualisation of the average pathway of sound by the acoustic intensity helps the interpretation of the modal amplitude data. The problem chosen for the presentation deals with the propagation of a single acoustic mode upstream through the tapering inlet duct of a centrifugal compressor. The propagation of tone noise is a typical problem for computational aeroacoustics. The numerical approach employs high-order finite-difference discretisation schemes with structured body-fitted meshes. An overset grid approach allows to overcome the geometrical complexity of the problem. The conservation of the acoustic energy is found to be violated by less than 3% in case of a potential base flow. In this case major sources of error are found in the interpolation between overset and background mesh. In case of a non-potential flow with boundary layers at the wall, the conservation of acoustic energy cannot be claimed. Consequently, it shows an increase of the acoustic energy, for which the accelerated flow in the nozzle is identified as source. It is shown that the filtering scheme affect the solution more than the spatial discretisation, if the grid resolution is relatively high. A strong scattering of energy into higher radial modes is detected. The fifth and sixth radial mode are found to be preferred in the current example. They are excited in the nozzle with a similar level. For these high radial modes, the transport of acoustic energy takes place further away from the duct wall. This explains the relatively large drop of about 20dB for the average sound pressure level at the wall over the inlet nozzle. [Copyright &y& Elsevier]

An acoustic intensity-based method (AIBM) is extended and verified for predicting sound radiation in a subsonic uniform flow. The method assumes that the acoustic propagation is governed by the modified Helmholtz equation on and outside of a control surface, which encloses all the noise sources and nonlinear effects. With acoustic pressure derivative and its co-located acoustic pressure as input from an open control surface, the unique solution of the modified Helmholtz equation is obtained by solving the least squares problem. The AIBM is coupled with near-field Computational Fluid Dynamics (CFD)/Computational Aeroacoustics (CAA) methods to predict sound radiation of model aeroacoustic problems. The effectiveness of this hybrid approach has been demonstrated by examples of both tonal and broadband noise. Since the AIBM method is stable and accurate based on the input acoustic data from an open surface in a radiated field, it is therefore advantageous for the far-field prediction of aerodynamics noise propagation when an acoustic input from a closed control surface, like the Ffowcs Williams–Hawkings surface, is not available [Philos. Trans. R. Soc. London, Ser. A 264, 321–342 (1969)]. [ABSTRACT FROM AUTHOR]

Abstract: The effect of acoustic streaming (more precisely the Eckart streaming) on the linear stability of a laterally heated fluid layer confined between two horizontal infinite walls (Hadley flow) has been studied. In the considered range of Prandtl number (), three types of instabilities prevail in the absence of acoustic streaming: two-dimensional stationary instabilities for low Prandtl numbers, and three-dimensional oscillatory and then stationary instabilities for higher Prandtl numbers. When an acoustic beam of width (normalized by the layer depth) is applied, the thresholds of the two-dimensional modes, which become oscillatory, increase with the acoustic intensity (monitored through the parameter A) before strongly decreasing to reach the pure acoustic streaming instability threshold. Concerning the three-dimensional instabilities, the thresholds of the oscillatory modes increase while those of the stationary modes strongly decrease. For , these evolutions induce the crossing of the critical curves of these two modes when A is increased, so that the oscillatory modes which are dominant for small values of A are replaced by the stationary modes for larger values of A. The position of the crossing depends on the width of the acoustic beam. To cite this article: W. Dridi et al., C. R. Mecanique 337 (2009). [Copyright &y& Elsevier]

In April 1989 an acoustic experiment was carried out over the abyssal plain south of Madeira in which transmissions were made, for about an hour, at 482, 680, and 740 Hz from a ship steaming at 5 Kn to a receiving array towed by another ship 65 km away traveling on a parallel course at the same speed. The signals arrived by two paths, an upper path trapped in the surface duct and a lower path via the main sound channel. This paper describes the experiment and analyses of the intensity fluctuations in the signal received by the lower path. This allows the authors to investigate the horizontal structure of acoustic intensity fluctuations in the ocean when these are due principally to internal waves. This aspect of such acoustic intensity fluctuations has received little attention until now. The experimental results are compared with theoretical predictions based on the parabolic moment equations for propagation and scattering in randomly irregular media, and on the standard Garrett–Munk model for ocean internal waves. The experimental results and theoretical predictions agree quite well but the comparison also raises some new questions, in particular, about the correlation of intensity fluctuations as the acoustic transmission frequency is varied. [ABSTRACT FROM AUTHOR]

Two-sensor method proposed by Fusco et al. [“Two-sensor power measurements in lossy ducts,” J. Acoust. Soc. Am. 91, 2229–2235 (1992)] is a novel technique that determines acoustic intensity of a gas column in a wide duct from measurements of pressure based on the boundary layer approximation. For further development of this method, its validity is experimentally tested through comparison with the direct method measuring the pressure and the velocity simultaneously, and its formulation is modified to include the narrow duct range where the duct radius is smaller than the viscous boundary layer thickness of the gas. It is shown that the modified two-sensor method enables quick and accurate evaluation of the acoustic intensity seamlessly from narrow to wide duct ranges. [ABSTRACT FROM AUTHOR]

An acoustic intensity-based method is proposed for the reconstruction of acoustic radiation pressure. Unlike the traditional inverse acoustic methods, the proposed method includes the acoustic pressure gradient as an input in addition to its simultaneous, co-located acoustic pressure in a radiated field. As a result, the reconstruction of acoustic radiation pressure from the input acoustic data over a portion of a surface enclosing all the acoustic sources, i.e., an open surface, becomes unique due to the unique continuation theory of elliptic equations. Hence the method is more stable and the reconstructed acoustic pressure is less dependable on the locations of the input acoustic data. Furthermore, the proposed method can be applied for both inverse and forward problems up to the minimum sphere enclosing the sources of interest. The effectiveness of the method is demonstrated by the results of several acoustic radiation examples with single or multi-frequency source in a two-dimensional configuration. The results from the method also show a measurable improvement in accuracy and consistency of reconstructed acoustic radiation pressure, in particular when the effect of the signal-to-noise ratio is included. [ABSTRACT FROM AUTHOR]

A new approach for characterizing high intensity focused ultrasound (HIFU) transducers is presented. The technique is based upon the acoustic streaming field generated by absorption of the HIFU beam in a liquid medium. The streaming field is quantified using digital particle image velocimetry, and a numerical algorithm is employed to compute the acoustic intensity field giving rise to the observed streaming field. The method as presented here is applicable to moderate intensity regimes, above the intensities which may be damaging to conventional hydrophones, but below the levels where nonlinear propagation effects are appreciable. Intensity fields and acoustic powers predicted using the streaming method were found to agree within 10% with measurements obtained using hydrophones and radiation force balances. Besides acoustic intensity fields, the streaming technique may be used to determine other important HIFU parameters, such as beam tilt angle or absorption of the propagation medium. [ABSTRACT FROM AUTHOR]

Waveguide invariant theory is used to describe the frequency shifts of constant acoustic intensity level curves in broadband signal spectrograms measured at the New Jersey Shelf during the winter of 2003. The broadband signals (270–330 Hz) were transmitted from a fixed source and received at three fixed receivers, located at 10, 20, and 30 km range along a cross-shelf propagation track. The constant acoustic intensity level curves of the received signals indicate regular frequency shifts that can be well predicted by the change in water depth observed through tens of tidal cycles. A second pattern of frequency shifts is observed at only 30 km range where significant variability of slope-water intrusion was measured. An excellent agreement between observed frequency shifts of the constant acoustic intensity levels and those predicted by the change in tide height and slope water elevations suggests the capability of long-term acoustic monitoring of tide and slope water intrusions in winter conditions. [ABSTRACT FROM AUTHOR]

This paper describes a novel phenomenon "liquid needle" produced by the self-focusing acoustic transducer (SFAT). The SFAT is composed of a metal/piezo-material/metal plate (with and without a support layer) which has one side air backed while the other side is liquid backed. The SEAT generates and focuses acoustic waves (through wave interference) at the top surface of the liquid (with acoustic intensity up to 15W/cm²). The focused acoustic beam deforms the free liquid surface through the acoustic streaming effect, and produces a needle-shaped liquid column on the free liquid surface. With various SFATs and different types of liquids, we have obtained liquid needles that are 400-12 000 µm tall. The liquid needle diameter at its tip varies from less than 15 µm to more than 200 µm. [ABSTRACT FROM AUTHOR]

The article presents abstracts of current literature relating to shock and vibration. They include "Active control of noise from a vacuum cleaner," "Hermetically sealed oil-free turbocompressor technology," and "Near field acoustic holography (NAH) theory for cyclostationary sound field and its application."

Abstract: This note is written to correct an erroneous interpretation of acoustic intensity made by the authors during the writing of the paper “A field study of suspended frazil ice particles” by Brian Morse and Martin Richard. The correct interpretation is presented and the impacts on the findings are quantified. [Copyright &y& Elsevier]