Attenuation of ultrasound in suspensions of bovine muscle myofibrils and myosin

The attenuation of 1.5-7 MHz ultrasound was measured over the pH range 3-7 in 100 mM KCl suspensions of bovine M. semitendinosus myofibrils, precipitated myosin and the residue of myofibrils after partial extraction of myosin. In all fractions attenuation showed a similar dependence on pH over the range 3-7, with a broad, substantial maximum in the region of pH 4.5-pH 5.5 and similar mass attenuation coefficients (per g protein). At pH 7 and 7 MHz these were 3.49 +/- 0.20 cm2 g-1 in the myofibrils, 3.26 +/- 0.31 cm2 g-1 in the myofibrilar residue and 2.83 +/- 0.68 cm2 g-1 in the precipitated myosin. Measurements at 5.3 MHz of precipitated myosin over a wider pH range revealed an attenuation titration curve similar to that previously observed in homogenates of muscle and muscle myofibrils, with substantial peaks at about pH 5 and 11.5, and a shoulder perhaps indicating a small underlying peak at about pH 8-9. Myosin dissolved in 800 mM KCl gave attenuation levels that were typically 50% lower than precipitated myosin e.g. at pH 7 and 7 MHz: 2.83 +/- 0.68 cm2 g-1 in the precipitated form, 1.29 +/- 0.10 cm2 g-1 in solution. These results indicated that: (a) attenuation by myosin filaments contributed substantially to the total attenuation in suspensions of myofibrils and (b) the peak in the myofibrilar attenuation is caused, or substantially contributed to, by a process taking place in the myosin component.     

Ultrasound speed and attenuation in homogenates of bovine skeletal muscle

The attenuation and speed of ultrasound were measured in homogenates of post-rigor bovine skeletal muscle, and found to increase in proportion to the concentration of muscle. Extrapolation of the data to tissue concentrations yielded an attenuation of 7.5 dB cm-1 at pH 5.7, 20 degrees C and 7.3 MHz. This was close to that measured in the minced tissue, 8.3 dB cm-1, and between values previously recorded across and along the fibres of intact muscle. Corresponding measurements for the speed of ultrasound in homogenates, extrapolated to the native tissue concentration, were: 1555 +/- 9 m s-1 at 0 degree C, 1592 +/- 10 m s-1 at 20 degrees C and 1616 +/- 9 m s-1 at 37 degrees C. These were not significantly different from measurements of minced muscle at the same temperatures. Measurements of the attenuation of 7.3 MHz ultrasound in suspensions of myofibrils indicated that attenuation by the myofibrils caused at least 64% of the attenuation in muscle homogenates at pH 5.7. Re-analysis of the viscous loss arising from relative movement of the myofibrils in their surrounding fluid, indicated that this mechanism could account for no more than 15% of the attenuation in muscle homogenates. Attenuation due to scattering was calculated to be at least two orders of magnitude smaller than that observed in either homogenates or suspensions of myofibrils. It was concluded that the contribution of scattering to the attenuation was small, and that the attenuation was caused by processes involving an absorption of energy.(ABSTRACT TRUNCATED AT 250 WORDS)     

Attenuation of ultrasound in homogenates of bovine skeletal muscle and other tissues

The attenuation of ultrasound in homogenates of bovine skeletal muscle and suspensions of myofibrils was measured over the frequency range 1.5-7 MHz, and found to be proportional to protein concentration in both. In the homogenates it varied with frequency and temperature in a similar way to the attenuation in post rigor muscle tissue; myofibrils showed a higher frequency dependence. The attenuation in homogenates of bovine muscle, liver and kidney and in suspensions of myofibrils was measured over the pH range 3.5-13, and each showed a peak at about pH 11.5. This was thought to be due to a proton transfer process between NH3+ groups on the tissue proteins and OH- ions in the suspending fluid. A substantial peak at about pH 5 in the muscle and myofibril suspensions was not observed in homogenates of liver and kidney and was thought to be due to components of muscle that are absent from the other tissues. Myofibrils suspended in percoll solution of density 1.05 g cm-3, chosen to match approximately the density of the myofibrils, showed a slightly lower attenuation over the pH range 5-7, but a pH dependence similar to that of the myofibrils suspended in saline. The difference in the attenuations may be interpreted as the viscous component of the attenuation due to relative motion between the myofibril and its surrounding saline. The peak at pH 5 did not, however, appear to be due to the viscous loss mechanism peaking due to maximum shrinkage (and therefore maximum density) of the myofibril near this pH.(ABSTRACT TRUNCATED AT 250 WORDS)     

Theoretical analysis of sound attenuation mechanisms in blood and in erythrocyte suspensions.

A theoretical analysis of the effect of the elasticity of cell membranes on sound attenuation in blood and erythrocyte suspensions was carried out. It is shown that the shell model of a cell adequately describes the attenuation in red blood cell suspensions. The contribution of viscous drag losses to the sound attenuation decreases with frequency, and at a frequency of 1 MHz it can be as high as 44% in water suspensions of erythrocytes and 24% in blood.     

Ultrasonic wave properties in the particle compounded agarose gels

Ultrasonic wave properties (attenuation and velocity) in the particle compounded agarose gels have been experimentally studied in the range from 1 to 30 MHz. The particles used were talc, glass beads and graphite. The effects of size and volume concentration of particles were clearly observed as changes of ultrasonic wave properties. Applying the Urick's theory for viscous liquid suspensions, the specific curves of velocity in the gels were observed as a function of a beta, where a is the radius of the particles and beta is described by angular frequency omega, density rho and fluid viscosity eta. This indicates that the particle behavior in the gels seems to be similar with that in the viscous fluid. The estimated eta in the gels was higher than that of the free water, showing the high viscosity in the gels.     

Ultrasonic attenuation in red blood cell suspensions

A theoretical analysis of ultrasonic attenuation in aqueous suspensions of red blood cells was carried out. This verified the relative importance of several mechanisms: absorption accounts for 60% of the attenuation, viscous relative motion loss accounts for less than 30%, and the sound scattering contribution is negligible.     

Issues in the statistical mechanics of steady sedimentation

A critical review is presented of recent experimental and theoretical work on the steady sedimentation of particulate suspensions in viscous fluids. The point of view is that of a practitioner of non-equilibrium statistical physics rather than classical fluid mechanics.     

Orientational ordering of protein particles with asymmetric introductions of ferritin in a magnetic field

The mechanism of orientational ordering of protein particles in an inhomogeneous magnetic field, proposed by the authors in Phys. Wave Phenom. 13(1), 1 (2005), was extended to ferritin inclusions in such particles, taking into account the probable appearance of superantiferromagnetic susceptibility properties. Degrees of orientational ordering, ordered state formation and decay times achievable in bioparticle suspensions were estimated for a realistic model of the resistance to motion of elliptic particles in a viscous fluid. Biotechnological applications of the effect are discussed.     

Characterization of suspensions of particles in water by an ultrasonic resonant cell

This paper presents a resonant technique to accurately measure phase-velocity and attenuation of longitudinal acoustic waves in suspensions of solid particles in water. The technique is based on exciting thickness resonances of a layer of fluid and analyzing its spectrum. To this end, a resonant cell to contain the fluid is described and used. Two different type of water suspensions are studied: titanium dioxide and alumina particles; particle volume fraction is in the range 0–0.18. Simultaneous determination of particle size distribution in the suspension by an optical method are also carried out. Finally, the experimental results are compared with theoretical predictions obtained from three different approaches.     

High-frequency rolloff in a cochlear model without critical-layer resonance

Zwislocki's original cochlear model, incorporating axial fluid inertia and shunt basilar-membrane stiffness and viscous resistance, possesses an operating regime not previously emphasized in the literature. Even in the absence of basilar-membrane mass and the consequent critical-layer resonance, this regime provides extraordinarily steep high-frequency rolloff. That rolloff is not associated with a critical frequency at which energy flow velocity goes to zero, but is attributable instead to a combination of two effects; (1) frequency-dependent energy coupling to the basilar-membrane viscous resistance, leading to local attenuation of the traveling wave at a rate (Np/cycle) that is directly proportional to frequency, and (2) wavelength that decreases with increasing frequency, thus increasing the number of cycles per unit length of basilar membrane. This combination leads to local attenuation of the traveling-wave amplitude (hence energy absorption from the traveling wave) that is strongly dependent on frequency, the rate (Np/cm) being proportional to the square of frequency in the long-wave mode. In Ranke's (two-dimensional, short-wave mode) version of the model, the same operating regime leads to attenuation that is even more intensely dependent on frequency, the rate being proportional to the cube of frequency.     

Attenuation of ultrasound in milks and creams

Measurements of the attenuation of 1.5 to 7 MHz ultrasound in milks and creams, aqueous solutions of milk proteins and milk fat demonstrated that the attenuation due to the fat component was proportional to the fat concentration (at low volume fractions, less than 4%) and was caused by two effects: losses arising from its particulate nature and intrinsic attenuation (mass attenuation coefficient 1.1 cm² g⁻¹ at 7 MHz in pure milk fat). Comparison with theoretical equations showed that absorption by thermal conduction dominated the particulate losses and increased with decreasing fat globule size, over the range 1.5 to 7 MHz. This was confirmed by examining milks homogenized to different degrees. The losses in the non-fat components were mainly due to the protein components which also probably dominated the shape of the attenuation titration curves for skimmed milk, producing peaks in attenuation in the range pH 4–4.5 and about pH 11.3.     

An Exotic Phase Change in Dynamic Electrorheological Fluids

It is well known that constant or time-varying electric fields can induce phase changes in electrorheological(ER) fluids, from a liquid to semi-solid state, provided the field strength is larger than some critical value. We describe here an experimental and theoretical study considering yet a different class of phase changes, specifically those for an ER fluid in the presence of both shear flow and a time-varying electric field. We note that as the frequency of the field is decreased, the ER fluid will go from a liquid to an intermediate transition state, and eventually to a shear banding state. Our theoretical analysis further indicates that this phase change originates from competing effects of viscous and electrical forces. Ultimately, we conclude that it is possible to achieve various states and corresponding(desired)macroscopic properties of dynamic colloidal suspensions by adjusting the frequency of the externally applied electric field.     

Application of surface and normal ultrasonic waves for measuring the parameters of technical fluids: II. Density measurements

The effect of a fluid on the surface waves moving in a waveguide along its boundary with the fluid is considered. The effect of the shear and volume viscosities of the fluid on the damping coefficient of such a surface wave is estimated. It is shown that the effect of fluids may be neglected at a measurement accuracy of about 10^?3 if their shear viscosities are lower than 0.1 Pa s. At a higher viscosity, corrections that take into account the contribution of viscous losses to the measured damping coefficient of a surface wave should be introduced. A technique for calibrating a density sensor for low-viscosity fluids is described, and the densities of NaCl and saccharose solutions in distilled water are measured. The experimental results agree qualitatively with the theoretical estimates. It is noted that this method of measuring the longitudinal impedance of a fluid can use the same apparatus design in both the principle (pulsed) and the frequency range (1?C10 MHz) for measuring the density, both viscosities, the velocity, and the sound absorption coefficient of a fluid. This design almost coincides with the apparatus used in the means of nondestructive quality control of materials and articles.     

An acoustic study of soils that model seabed sediments containing gas bubbles

The acoustic response of gassy seabed sediment is unique. It is a dispersive and extraordinarily attenuative natural material at frequencies which cause gas bubble resonance. It conceals the structure of the seabed from seismic profiling and it dampens acoustic signals that, for example, trigger acoustic mines. In the past, theoretical studies have formulated the probable cause of this response and crude experimental work has partially corroborated theory. This study measures compressional wave velocity and attenuation in a laboratory soil simulating natural gassy soil, and it investigates the structural properties that cause the unique acoustic response. It was confirmed that below the frequencies which cause resonance the soil behaves as a compressible material (containing gas), and above as a relatively incompressible material (containing no gas). Over the frequency range producing bubble resonance it is suggested that the soil should be modeled as a biphasic material of gas and a relatively incompressible saturated soil matrix (particles and fluid). Velocities for gassy soil were found to be as low as 220 m/s at frequencies below resonance and 1500 m/s above resonance; attenuations were found to be as high as 60 dB/cm for moderately gassy soil and as low as 1 dB/cm for soil with almost no gas.     

Scattering of sound in a moving viscous microinhomogeneous medium at large Reynolds numbers

A generalization of the Rayleigh law of a low-frequency sound attenuation in a microinhomogeneous medium to the case of scattering particles moving in a viscous liquid at a large Reynolds numbers is proposed. It is shown that, under these conditions, the attenuation may be independent of the scattering by the moving particles themselves but be only determined by the flow caused by these particles, the maximum attenuation being observed in the direction across the particle motion. The corresponding corrections proportional to the first power of the hydrodynamic Mach number are compared with the corrections lying at the basis of the modified Rayleigh law, which was proposed earlier for the potential flow of an ideal liquid around inhomogeneities, and also with the laws of scattering in a moving viscous microinhomogeneous medium at a small Reynolds numbers. As an example of the operation of the generalized law, characteristics of the sound scattering by rain are refined.     

高密度超细颗粒高浓度悬浊液超声衰减的数值模拟分析

以拓展耦合相ECP理论模型为基础,通过对高浓度超细二氧化钛-水悬浊液和玻璃微珠-水悬浊液中超声衰减的数值计算分析,讨论了高密度差异颗粒两相介质在高浓度情况下,超声频率、颗粒粒径大小、颗粒浓度对超声波衰减的影响,为高密度超细颗粒在高浓度悬浊液中颗粒粒度和浓度的超声波测量提供理论支持。     

Polydisperse particle size characterization by ultrasonic attenuation spectroscopy in the micrometer range

The theoretical advantages of ultrasonic attenuation spectroscopy for particle size are currently not fully utilized. Especially in the region of larger particles, there is a lack of experimental confirmation of applicable models which may be used to infer particle sizes from measured attenuation spectra. With the present work, an attempt is made to supply experimental data, obtained with a commercially available ultrasonic attenuation spectrometer, and model calculations, which are based on the resonant scattering theory. It is shown that measured attenuation results for various combinations of disperse and continuous phase for both polydisperse emulsions and suspensions are reproducible by calculation. The approach is further examined for suspensions of porous particles. Here, the resonant scattering approach is combined with the Biot model for poroelasticity to obtain attenuation results with several fractions of titania aggregates, differing in particle size and pore diameter. The results indicate that the theory of resonant scattering is a valid approach if applied to particle size characterization in the large particle limit.     

Determination of optical parameters of pulp suspensions by time-resolved detection of photoacoustic signals and total diffuse reflectance measurements

Time-resolved photoacoustics were used to measure the optical parameters of pulp suspensions for the first time. Reconstructing stress distribution along the direction of the incident laser light allows the effective attenuation coefficient of these suspensions to be determined. Simultaneously, the total diffuse reflectance of the suspensions was measured by the same laser source. Based on the effective attenuation coefficient and total diffuse reflectance, the absorption and reduced scattering coefficients of pulp suspensions can be calculated. In this study, three kinds of pulp suspensions with different kappa number (2, 13, and 16), a measure of lignin content in pulp fibers, were diluted with water to make samples with a consistency range from 1% to 5%, and studied at 355 nm wavelength. The results showed that the optical coefficients were approximately proportional to pulp consistency; on the other hand, the absorption coefficient was linearly correlated with kappa number, but the reduced scattering coefficient was not. Therefore, by determining its optical parameters, it is possible to extract the consistency and kappa number of an unknown pulp suspension.     

Impact of local attenuation approximations when estimating correlation length from backscattered ultrasound echoes

Estimating the characteristic correlation length of tissue microstructure from the backscattered power spectrum could improve the diagnostic capability of medical ultrasound. Previously, size estimates were obtained after compensating for source focusing, the frequency-dependent attenuation along the propagation path (total attenuation), and the frequency-dependent attenuation in the scattering region (local attenuation). In this study, the impact of approximations of the local attenuation on the scatterer size estimate was determined using computer simulations and theoretical analysis. The simulations used Gaussian impedance distributions with an effective radius of 25 microm randomly positioned in a homogeneous half-space sonified by a spherically focused source (f/1 to f/4). The approximations of the local attenuation that were assessed neglected local attenuation (i.e., assume 0 dB/cm-MHz) neglected frequency dependence of the local attenuation, and assumed a finite frequency dependence (i.e., 0.5 dB/cm-MHz) independent of the true attenuation of the medium. Errors in the scatterer size estimate due to the local attenuation approximations increased with increasing window length, increasing true local attenuation and increasing f number. The most robust estimates were obtained when the local attenuation was approximated by a tissue-independent attenuation value that was greater than 70% of the largest attenuation expected in the tissue region of interest.