Changes In Sound Speed Research Articles

A wave equation model for retrograde media with a bubble structure

A nonlinear wave equation is obtained for liquid-vapor mixtures with regard to arbitrary change of equilibrium sound speed in a mixture with growth and condensation of vapor bubbles, which has a limit transition to a wave equation for pure liquid at full collapse of vapor cavities. A particular case of a collapsing wave equation (CWE) of retrograde media is considered, e.g., liquid-vapor media with low vaporization heat and low dissipation, observed near the critical liquid-vapor point, where the main effect is variable sound speed. Based on the CWE numerical solutions it is shown that in such liquid-vapor media, one can observe previously unknown nonlinear wave structures with depression waves.

Extracting changes in air temperature using acoustic coda phase delays

Blast waves produced by 60 high-explosive detonations were recorded at short distances (few hundreds of meters); the corresponding waveforms show charge-configuration independent coda-like features (i.e., similar shapes, amplitudes, and phases) lasting several seconds. These features are modeled as reflected and/or scattered waves by acoustic reflectors/scatters surrounding the explosions. Using explosion pairs, relative coda phase delays are extracted and modeled as changes in sound speed due to changes in air temperature. Measurements from nearby weather towers are used for validation.

Detecting hepatic steatosis using ultrasound-induced thermal strain imaging: an ex vivo animal study

Hepatic steatosis or fatty liver disease occurs when lipids accumulate within the liver and can lead to steatohepatitis, cirrhosis, liver cancer and eventual liver failure requiring liver transplant. Conventional brightness mode (B-mode) ultrasound (US) is the most common noninvasive diagnostic imaging modality used to diagnose hepatic steatosis in clinics. However, it is mostly subjective or requires a reference organ such as the kidney or spleen with which to compare. This comparison can be problematic when the reference organ is diseased or absent. The current work presents an alternative approach to noninvasively detecting liver fat content using US-induced thermal strain imaging (US-TSI). This technique is based on the difference in the change in the speed of sound as a function of temperature between water- and lipid-based tissues. US-TSI was conducted using two system configurations including a mid-frequency scanner with a single linear array transducer (5–14 MHz) for both imaging and heating and a high-frequency (13–24 MHz) small animal imaging system combined with a separate custom-designed US heating transducer array. Fatty livers (n = 10) with high fat content (45.6 ± 11.7%) from an obese mouse model and control livers (n = 10) with low fat content (4.8 ± 2.9%) from wild-type mice were embedded in gelatin. Then, US imaging was performed before and after US induced heating. Heating time periods of ∼3 s and ∼9.2 s were used for the mid-frequency imaging and high-frequency imaging systems, respectively, to induce temperature changes of approximately 1.5 °C. The apparent echo shifts that were induced as a result of sound speed change were estimated using 2D phase-sensitive speckle tracking. Following US-TSI, histology was performed to stain lipids and measure percentage fat in the mouse livers. Thermal strain measurements in fatty livers (−0.065 ± 0.079%) were significantly (p < 0.05) higher than those measured in control livers (−0.124 ± 0.037%). Using histology as a gold standard to classify mouse livers, US-TSI had a sensitivity and specificity of 70% and 90%, respectively. The area under the receiver operating characteristic curve was 0.775. This ex vivo study demonstrates the feasibility of using US-TSI to detect fatty livers and warrants further investigation of US-TSI as a diagnostic tool for hepatic steatosis.

Mechanism Study of Acoustics Method for Dryness Measuring and Model Establishment

Combining acoustic theory and thermodynamic properties of water and steam, the density and sound velocity change with pressure and temperature, and the acoustic wave at the same temperature, the same pressure of gas-liquid two phase flow in the corresponding content of different causes the sound speed change are studied.. Set up steam model formula and the speed of sound, results showed that, water and water vapor velocity and density affected by temperature, pressure changes are different, steam quality measurement by acoustic method is feasible.

Acoustic mode coupling induced by nonlinear internal waves: evaluation of the mode coupling matrices and applications.

This paper applies the mode coupling equation to calculate the mode-coupling matrix for nonlinear internal waves appearing as a train of solitons. The calculation is applied to an individual soliton up to second order expansion in sound speed perturbation in the Dyson series. The expansion is valid so long as the fractional sound speed change due to a single soliton, integrated over range and depth, times the wavenumber is smaller than unity. Scattering between the solitons are included by coupling the mode coupling matrices between the solitons. Acoustic fields calculated using this mode-coupling matrix formulation are compared with that obtained using a parabolic equation (PE) code. The results agree very well in terms of the depth integrated acoustic energy at the receivers for moving solitary internal waves. The advantages of using the proposed approach are: (1) The effects of mode coupling can be studied as a function of range and time as the solitons travel along the propagation path, and (2) it allows speedy calculations of sound propagation through a packet or packets of solitons saving orders of magnitude computations compared with the PE code. The mode coupling theory is applied to at-sea data to illustrate the underlying physics.

Flexible integration of high-imaging-resolution and high-power arrays for ultrasound-induced thermal strain imaging (US-TSI).

Ultrasound-induced thermal strain imaging (USTSI) for carotid artery plaque detection requires both high imaging resolution (<100 μm) and sufficient US-induced heating to elevate the tissue temperature (~1°C to 3°C within 1 to 3 cardiac cycles) to produce a noticeable change in sound speed in the targeted tissues. Because the optimization of both imaging and heating in a monolithic array design is particularly expensive and inflexible, a new integrated approach is presented which utilizes independent ultrasound arrays to meet the requirements for this particular application. This work demonstrates a new approach in dual-array construction. A 3-D printed manifold was built to support both a high-resolution 20 MHz commercial imaging array and 6 custom heating elements operating in the 3.5 to 4 MHz range. For the application of US-TSI in carotid plaque characterization, the tissue target site is 20 to 30 mm deep, with a typical target volume of 2 mm (elevation) × 8 mm (azimuthal) × 5 mm (depth). The custom heating array performance was fully characterized for two design variants (flat and spherical apertures), and can easily deliver 30 W of total acoustic power to produce intensities greater than 15 W/cm(2) in the tissue target region.

An inverse method for estimating sediment sound speed

A fast approach for solving the inverse problem of estimating sediment sound-speed based on the Deift-Trubowitz trace formula is being investigated in our research. Under certain assumptions, this algorithm can recover the sound speed profile in the seabed using pressure field measurements in the water column at low frequencies. The inversion algorithm, employing a modified Born approximation, works well with synthetic data. Results are compared to those of previously developed methods and demonstrate improvement especially at sharp changes in sound speed. Although the method is stable and effective with noise-free data, problems arise when noise is considered. In our work, we develop regularization methods to remedy this problem. Finally, we recognize that some assumptions necessary for this algorithm to work may not be realistic; we discuss ways to relax these limitations. [Work supported by ONR.]

Long-range asymptotic behavior of vertical travel-time sensitivity kernels

Vertical travel-time sensitivity kernels (VTSKs) describe the effect of horizontally uniform sound-speed changes on travel times in range-independent ocean environments. Wave-theoretic VTSKs can be obtained either analytically, through perturbation of the normal-mode representation, or numerically, as horizontal marginals of the corresponding two-dimensional and three-dimensional travel-time sensitivity kernels. In previous works, it has been observed that wave-theoretic finite-frequency VTSKs approach the corresponding ray-theoretic sensitivity kernels as the propagation range increases. The present work is an attempt to explain this behavior. A stationary-phase approach is used to obtain a long-range asymptotic expression for the wave-theoretic VTSKs. The resulting asymptotic VTSKs are very close to the corresponding ray-theoretic ones. The smoothness condition, required for the stationary-phase approximation to hold, is used to obtain an estimate for the range beyond which the asymptotic behavior sets in.

Creation and Characterization of an Ultrasound and CT Phantom for Noninvasive Ultrasound Thermometry Calibration

Ultrasound thermometry provides noninvasive 2-D temperature monitoring, and in this paper, we have investigated the use of computed tomography (CT) radiodensity to characterize tissues to improve the accuracy of ultrasound thermometry. Agarose-based tissue-mimicking phantoms were created with glyceryl trioleate (a fat-mimicking material) concentration of 0%, 10%, 20%, 30%, 40%, and 50%. The speed of sound (SOS) of the phantoms was measured over a temperature range of 22.1-41.1 °C. CT images of the phantoms were acquired by a clinical dedicated breast CT scanner, followed by calculation of the Hounsfield units (HU). The phantom was heated with a therapeutic acoustic pulse (1.54 MHz), while RF data were acquired with a 10-MHz linear-array transducer. Two-dimensional speckle tracking was used to calculate the thermal strain offline. The tissue-dependent thermal strain parameter required for ultrasound thermometry was analyzed and correlated with CT radiodensity, followed by the validation of the temperature prediction. Results showed that the change in SOS with the temperature increase was opposite in sign between the 0%-10% and 20%-50% trioleate phantoms. The inverse of the tissue-dependent thermal strain parameter of the phantoms was correlated with the CT radiodensity (R(2) = 0.99). A blinded ultrasound thermometry study on phantoms with a trioleate range of 5%-35% demonstrated the capability to estimate the tissue-dependent thermal strain parameter and estimate temperature with error less than ~1 °C. In conclusion, CT radiodensity may provide a method for improving ultrasound thermometry in heterogeneous tissues.

Stability, metastability, and elastic properties of a dense silica polymorph, seifertite

Dense silica polymorphs with sixfold coordinated Si have been found in SNC and lunar meteorites and may be important minerals for silica‐rich components in the lower mantle. However, the stable crystal structure in the lower mantle and properties of dense silica remain controversial. Under stable heating and quasi‐hydrostatic stress conditions, we found that the CaCl2 type undergoes a phase transition to the α‐PbO2type (seifertite) at 130–140 GPa and 2500 K. Our data suggest that this phase transition occurs at a greater depth than the perovskite → postperovskite transition in the lowermost mantle. The molar volume measured at 1 bar is the smallest among the reported silica polymorphs, therefore having the highest calculated density and in excellent agreement with recent first‐principles calculations. The greater molar volume of seifertite found in the shergottite meteorite and previous experiments supports a metastable synthesis of the phase outside its stability field. Our data combined with the Hugoniots of silica polymorphs also rule out the possibility of the formation of seifertite in the meteorite within its stability field. We found very little change in bulk sound speed across the CaCl2‐type → seifertite transition. If shear wave velocity decreases at the transition to seifertite as suggested by some computational studies, this silica transition may provide an alternative explanation for the discontinuities with a shear wave velocity decrease found at depths greater than the D″discontinuity.

Assessing the low frequency acoustic characteristics of Macrocystis pyrifera, Egregia menziessi, and Laminaria solidungula

The acoustic properties of kelp forests are not well known, but are of interest for the development of environmental remote sensing applications. This study examined the low-frequency (0.2-4.5 kHz) acoustic properties of three species of kelp (Macrocystis pyrifera, Egregia menziessi, and Laminaria solidungula) using a one-dimensional acoustic resonator. Acoustic observations and measurements of kelp morphology were then used to test the validity of Wood's multi-phase medium model in describing the acoustic behavior of the kelp. For Macrocystis and Egregia, the two species of kelp possessing pneumatocysts, the change in sound speed was highly dependent on the volume of free air contained in the kelp. The volume of air alone, however, was unable to predict the effective sound speed of the multi-phase medium using a simple two-phase (air + water) form of Wood's model. A separate implementation of this model (frond + water) successfully yielded the acoustic compressibility of the frond structure for each species (Macrocystis = 1.39 ± 0.82 × 10(-8) Pa(-1); Egregia = 2.59 ± 5.75 × 10(-9) Pa(-1); Laminaria = 8.65 ± 8.22 × 10(-9) Pa(-1)). This investigation demonstrates that the acoustic characteristics of kelp are species-specific, biomass-dependent, and differ between species with and without pneumatocyst structures.

Characterizing an Agar/Gelatin Phantom for Image Guided Dosing and Feedback Control of High-Intensity Focused Ultrasound

The temperature dependence of an agar/gelatin phantom was evaluated. The purpose was to predict the material property response to high-intensity focused ultrasound (HIFU) for developing ultrasound guided dosing and targeting feedback. Changes in attenuation, sound speed, shear modulus and thermal properties with temperature were examined from 20°C to 70°C for 3 weeks post-manufacture. The attenuation decreased with temperature by a power factor of 0.15. Thermal conductivity, diffusivity and specific heat all increased linearly with temperature for a total change of approximately 16%, 10% and 6%, respectively. Sound speed had a parabolic dependence on temperature similar to that of water. Initially, the shear modulus irreversibly declined with even a slight increase in temperature. Over time, the gel maintained its room temperature shear modulus with moderate heating. A stable phantom was achieved within 2 weeks post-manufacture that possessed quasi-reversible material properties up to nearly 55°C.

High Beta-Palmitate Formula and Bone Strength in Term Infants: A Randomized, Double-Blind, Controlled Trial

We aimed to compare the effect of 12-week feeding of commercially available infant formulas with different percentages of palmitic acid at sn-2 (beta-palmitate) on anthropometric measures and bone strength of term infants. It was hypothesized that feeding infants with high beta-palmitate (HBP) formula will enhance their bone speed of sound (SOS). Eighty-three infants appropriate for gestational age participated in the study; of these, 58 were formula-fed and 25 breast-fed infants, serving as a reference group. The formula-fed infants were randomly assigned to receive HBP formula (43 % of the palmitic acid is esterified to the middle position of the glycerol backbone, study group; n = 30) or regular formula with low-beta palmitate (LBP, 14 % of the palmitic acid is esterified to the middle position of the glycerol backbone, n = 28). Sixty-six infants completed the 12-week study. Anthropometric and quantitative ultrasound measurements of bone SOS for assessment of bone strength were performed at randomization and at 6 and 12 weeks postnatal age. At randomization, gestational age, birth weight, and bone SOS were comparable between the three groups. At 12 weeks postnatal age, the mean bone SOS of the HBP group was significantly higher than that of the LBP group (2,896 ± 133 vs. 2,825 ± 79 m/s respectively, P = 0.049) and comparable with that of the breast-fed group (2,875 ± 85 m/s). We concluded that infants consuming HBP formula had changes in bone SOS that were comparable to those of infants consuming breast milk and favorable compared to infants consuming LBP formula.

동해에서 저주파 음파전파에 미치는 난수성 소용돌이의 영향

It is well known that sound waves in the sea propagates under the influence of sea surface and bottom roughness, the sound speed profile, the water depth, and the density of sea floor sediment. In particular, an abrupt change of sound speed with depth can greatly affect sound propagation through an eddy. Eddies are frequently generated in the East Sea near the Korean Peninsula. A warm eddy with diameter of about 150 km is often observed, and the sound speed profile is greatly changed within about 400 m of water depth at the center by the eddy around the Ulleung Basin in the East Sea. The characteristics of low-frequency sound propagation across a warm eddy are investigated by a sound propagation model in order to understand the influence of warm eddies. The acoustic rays and propagation losses are calculated by a range-dependent acoustic model in conditions where the eddy is both present and absent. We found that low-frequency sound propagation is affected by the warm eddy, and that the phenomena dominate the upper ocean within 800 m of water depth. The propagation losses of a 100 Hz frequency are variable within <TEX>${\pm}15$</TEX> dB with depth and range by the warm eddy. Such variations are more pronounced at the deep source near the sound channel axis than the shallow source. Furthermore, low-frequency sound propagation from the eddy center to the eddy edge is more affected by the warm eddy than sound propagation from the eddy edge to the eddy center.

On the significance of density‐induced speed of sound variations on US‐guided radiotherapy

To show the effect of speed of sound (SOS) aberration on ultrasound guided radiotherapy (US-gRT) as a function of implemented workflow. US systems assume that SOS is constant in human soft tissues (at a value of 1540 m∕s), while its actual nonuniform distribution produces small but systematic errors of up to a few millimeters in the positions of scanned structures. When a coregistered computerized tomography (CT) scan is available, the US image can be corrected for SOS aberration. Typically, image guided radiotherapy workflows implementing US systems only provide a CT scan at the simulation (SIM) stage. If changes occur in geometry or density distribution between SIM and treatment (TX) stage, SOS aberration can change accordingly, with a final impact on the measured position of structures which is dependent on the workflow adopted. Four basic scenarios were considered of possible changes between SIM and TX: (1) No changes, (2) only patient position changes (rigid rotation-translation), (3) only US transducer position changes (constrained on patient's surface), and (4) patient tissues thickness changes. Different SOS aberrations may arise from the different scenarios, according to the specific US-gRT workflow used: intermodality (INTER) where TX US scans are compared to SIM CT scans; intramodality (INTRA) where TX US scans are compared to SIM US scans; and INTERc and INTRAc where all US images are corrected for SOS aberration (using density information provided by SIM CT). For an experimental proof of principle, the effect of tissues thickness change was simulated in the different workflows: a dual layered phantom was filled with layers of sunflower oil (SOS 1478 m∕s), water (SOS 1482 m∕s), and 20% saline solution (SOS 1700 m∕s). The phantom was US scanned, the layer thicknesses were increased and the US scans were repeated. The errors resulting from the different workflows were compared. Theoretical considerations show that workflows implementing SOS correction based on SIM-CT scan (INTERc, INTRAc) give null errors in all scenarios except when tissues thickness changes, where an error proportional to the degree of change in SOS maps between SIM and TX (ΔSOS) occurs. An uncorrected workflow such as INTER produces in all scenarios a pure SOS error, while uncorrected INTRA produces a null error for rotation-translation of the patient, a ΔSOS error for changing tissues thickness and an error proportional to the degree of SOS distribution change along the different lines of view when shifting the transducer. The dual layered phantom demonstrated experimentally that the effect of SOS change between SIM and TX is clinically nonrelevant, being less than the intrinsic resolution of imaging systems, even when a substantial change in thicknesses is applied, provided that a SIM-CT-based SOS aberration correction is applied. Noncorrected workflows produce errors up to 4 mm for INTER and to 3 mm for INTRA in the phantom test. A SOS correction is advantageous for all US-gRT workflows and clinical cases, where the effect of SOS change can be considered a second order effect.

Controllable acoustic media having anisotropic mass density and tunable speed of sound

We present an experimental demonstration of a reconfigurable acoustic metafluid having anisotropic, actively controllable speed of sound for ultrasonic waves. The acoustic metamaterial is based upon suspensions of subwavelength discoid particles whose orientation and interparticle interactions are manipulated by external magnetic fields. Measured sound speeds are direction- and frequency-dependent, changing in a nonlinear fashion with particle concentration when an external magnetic field is applied. The observed changes in sound speed are significantly greater than that expected for suspensions of oriented but non-interacting oblate-spheroidal particles, suggesting that interactions between particles are important even for particle volume fractions below 0.5%.

SOLAR CYCLE VARIATION OF SOUND SPEED INSIDE THE SUN

Empirical radial profiles of the changes in sound speed inside the Sun between solar minimum and solar maximum have been extracted from Michelson Doppler Imager data by Baldner & Basu and Rabello-Soares. Here, we compare these results with the theoretical radial profiles predicted by a model of magnetic inhibition of convective onset: In the model, the degree of magnetic inhibition is characterized by a parameter δ, which is essentially the ratio of magnetic pressure to gas pressure. We find that the theoretical profiles overlap significantly with the empirical results in the outer half of the convection zone. But differences in the deeper layers indicate that the model needs to be modified there. The main result that emerges in the present comparison is that the value of δ must be larger near the surface than at great depth. A secondary result is that, in the course of the solar cycle, the magnetic field magnitude at the base of the convection zone may be out of phase with the field near the surface.

A long-term seafloor experiment using an acoustic ranging system: Precise horizontal distance measurements for detection of seafloor crustal deformation

We have developed a seafloor acoustic ranging system to monitor local seafloor crustal deformation. In August 2007 we carried out an experiment to estimate the long-term stability of acoustic measurements collected by the system. We deployed four precision acoustic transponders with about 920m and 590m spacing at the depth of 2035m in Kumano-nada, southeast coast Japan, and we collected acoustic ranges for 4months. The observed round-trip travel times showed a variation with peak-to-peak amplitude of about 0.75m in the range. It was confirmed that most of the variation could be explained by changes in sound speed. The standard deviation in the acoustic measurements was about 1.0cm after the correction for sound speed, and the average value of the ranges remained constant within 1cm.

Recent Progress in Thin 3He–4He Films

We review recent work on the properties of 3He–4He thin film mixtures. The subject is introduced by reviewing the contributions made by Gasparini and co-workers. In the first part of this survey, we examine a microscopic calculation of the effects that an adsorbed 3He component has on the collective excitations associated with a 4He film, third sound. The work in question computes the change in the third sound velocity due to adding 3He, and we can compare this with existing experiment. For small 3He coverage, the change in the third sound speed depends on the derivatives of the species chemical potentials with respect to the areal density. The microscopic calculation shows oscillations in the third sound speed that reflect the layered structure of the film. In the second part of this survey, we concentrate on the 3He component. An important impact of the 4He environment is to change the bare mass in the limit of zero 3He concentration to a hydrodynamic mass. Quasiparticle interactions are introduced through the Landau parameters. Our Landau parameters are determined by fitting s-wave and p-wave T-matrix components using experimental results for the effective mass and the spin susceptibility. We can then predict the thermodynamic behavior of the mixture films at finite polarization, and in addition we can predict the spectrum of zero-sound excitations at all polarizations.

Inelastic X-ray scattering in metallic glasses

The behavior of acoustic modes in solids can yield information on the glass dynamics at different length and frequency scales. Inelastic X-ray scattering (IXS) using Synchrotron radiation allows us to obtain detailed information on the sound speed behavior at different length scales as well as approaching the macroscopic limit. This gives an insight to the microscopic mechanisms responsible for the mechanical properties in the THz frequency domain. IXS also provides a method to investigate the fragility of glass-forming liquids via the non-ergodicity factor of the corresponding glasses. Moreover, some questions arise about how phenomena such as the polyamorphism, observed, e.g. in Ce55Al44 upon application of pressure, affect the mechanical properties of a metallic glass at a microscopic level. In this article we reveal a change in the high frequency response at the mesoscopic length scale with respect to the ultrasounds limit in metallic glasses. We will also review further applications of IXS on Pd and Ce-based metallic glasses to determine elastic constants, changes in sound speed due to polyamorphism and to investigate their fragility.