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1.
The shear wave velocity is measured in calibrated polymeric CIRS phantoms containing various spheres of two diameters located at different depths. The measurements are performed at the Verasonics ultrasound system using the method of the shear wave elasticity imaging. 相似文献
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The speed of the surface Rayleigh wave, which is related to the viscoelastic properties of the medium, can be measured by noninvasive and noncontact methods. This technique has been applied in biomedical applications such as detecting skin diseases. Static spherical indentation, which quantifies material elasticity through the relationship between loading force and displacement, has been applied in various areas including a number of biomedical applications. This paper compares the results obtained from these two methods on five gelatin phantoms of different concentrations (5%, 7.5%, 10%, 12.5% and 15%). The concentrations are chosen because the elasticity of such gelatin phantoms is close to that of tissue types such as skin. The results show that both the surface wave method and the static spherical indentation method produce the same values for shear elasticity. For example, the shear elasticities measured by the surface wave method are 1.51, 2.75, 5.34, 6.90 and 8.40 kPa on the five phantoms, respectively. In addition, by studying the dispersion curve of the surface wave speed, shear viscosity can be extracted. The measured shear viscosities are 0.00, 0.00, 0.13, 0.39 and 1.22 Pa.s on the five phantoms, respectively. The results also show that the shear elasticity of the gelatin phantoms increases linearly with their prepared concentrations. The linear regressions between concentration and shear elasticity have R2 values larger than 0.98 for both methods. 相似文献
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We study gelation under shear of aqueous gelatin by measuring the evolution of the apparent viscosity, thus extending the
previous study by de Carvalho and Djabourov (W. de Carvalho, M. Djabourov, Rheol. Acta 36, 591 (1997)). From a set of experiments under constant stress, we deduce that the microstructure evolves through the following
succession of regimes: i) nucleation and growth until crowding of a microgel suspension; ii) coalescence into strata parallel
to the flow; iii) gradual thickening of these strata via transverse cross-linking until the flow finally localizes into two
interfacial sliding bands which close sequentially. The transition between these regimes occurs at characteristic viscosity values. This scenario is fully confirmed by experiments performed at constant shear rates. We expect it to be relevant for
all materials forming thermoreversible gels. 相似文献
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Experimental results and theoretical estimates are presented to demonstrate the prospects of using the acoustic nonlinearity of a gel-like medium for increasing the efficiency of the shear wave generation in it by a pulsed ultrasonic beam. The experiment is based on the propagation of a focused beam of longitudinal acoustic waves at a frequency of 1.1 MHz in a gelatin sample and on the detection of shear waves by the optical method [1]. It is demonstrated that the amplitude of the shear wave excited by a nonlinear acoustic pulse can be increased by an order of magnitude owing to the formation of shock fronts in the profile of this pulse. 相似文献
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An on-line sensor to measure the density of a liquid or slurry, based on longitudinal wave reflection at the solid-fluid interface, has been developed by the staff at Pacific Northwest National Laboratory. The objective of this research is to employ shear wave reflection at the solid-fluid interface to provide an on-line measurement of viscosity as well. Both measurements are of great interest for process control in many industries. Shear wave reflection measurements were conducted for a variety of liquids. By analyzing multiple reflections within the solid (only 0.63 cm thick-similar to pipe wall thickness) we increased the sensitivity of the measurement. At the sixth echo, sensitivity was increased sufficiently and this echo was used for fluid interrogation. Shear wave propagation of ultrasound in liquids is dependent upon the viscosity and the shear modulus. The data are analyzed using the theory for light liquids (such as water and sugar water solutions) and also using the theory for highly viscous liquids (such as silicone oils). The results show that, for light liquids, the shear wave reflection measurements interrogate the viscosity. However, for highly viscous liquids, it is the shear wave modulus that dominates the shear wave reflection. Since the density is known, the shear wave velocity in the liquid can be determined from the shear wave modulus. The results show that shear wave velocities in silicone oils are very small and range from 315 to 2389 cm/s. Shear wave reflection measurements are perhaps the only way that shear wave velocity in liquids can be determined, because the shear waves in liquids are highly attenuated. These results show that, depending on the fluid characteristics, either the viscosity or the shear wave velocity can be used for process control. There are several novel features of this sensor: (1) The sensor can be mounted as part of the wall of a pipeline or tank or submerged in a tank. (2) The sensor is very compact and can be located within the process stream. (3) The sensor can interrogate and characterize very attenuative liquids or slurries because the sensor operation depends upon reflection at the interface between the solid and the fluid, rather than on transmission through a liquid. (4) The sensor performance is not affected by fluid flow rate, entrained air, or vibration. 相似文献
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The variations of phase velocity and normalized broadband ultrasonic attenuation (nBUA) with porosity were investigated in Polyacetal cuboid bone-mimicking phantoms with circular cylindrical pores running normal to the surface along the three orthogonal axes. The frequency-dependent phase velocity and attenuation coefficient in the phantoms with porosities from 0% to 65.9% were measured from 0.65 to 1.10 MHz. The results showed that the phase velocity at 880 kHz decreased linearly with porosity, whereas the nBUA increased linearly with porosity. This study provides a useful insight into the relationships between ultrasonic properties and porosity in bone at porosities lower than 70%. 相似文献
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We measure structure functions and structures in uniformly sheared strong turbulence using an array of hot-wire velocity sensors. We find that the large-scale shear persists down to the smallest scales. There is a marked asymmetry between velocity increments measured in the shear direction, and those measured in the plane perpendicular to it. In the shear direction the scaling exponents tend to a constant, signifying the presence of small-scale cliffs. Direct evidence for those is presented by the spatial structure of the strongest velocity gradients. 相似文献
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Barannik EA Girnyk A Tovstiak V Marusenko AI Emelianov SY Sarvazyan AP 《Ultrasonics》2002,40(1-8):849-852
In shear wave elasticity imaging (SWEI), mechanical excitation within the tissue is remotely generated using radiation force of focused ultrasound. The induced shear strain is subsequently detected to estimate visco-elastic properties of tissue and thus aid diagnostics. In this paper, the mechanical response of tissue to radiation force was detected using a modified ultrasound Doppler technique. The experiments were performed on tissue mimicking and tissue containing phantoms using a commercial diagnostic scanner. This scanner was modified to control both the pushing and probing beams. The pushing beam was fired repetitively along a single direction while interlaced probing beams swept the surrounding region of interest to detect the induced motion. The detectability of inhomogeneous inclusions using ultrasonic Doppler SWEI method has been demonstrated in this study. The displacement fields measured in elastic phantoms clearly reveal the oscillatory nature of the mechanical relaxation processes in response to impulsive load due to the boundary effects. This relaxation dynamics was also present in cooked muscle tissue, but was not detected in more viscous and less elastic phantom and raw muscles. Presence of a local heterogeneity in the vicinity of the focal region of the pushing beam results in generation of a standing wave field pattern which is manifested in the oscillatory response of the excited region of the tissue. There has been made an assumption that dynamic characteristics of the relaxation process may be used for visualization of inhomogeneities. 相似文献
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The statistical properties of velocity gradients in a wall-bounded turbulent channel flow are discussed on the basis of three-dimensional direct numerical simulations. Our analysis is concentrated on the trend of the statistical properties of the local enstrophy and the energy dissipation rate with increasing distance from the wall. We detect a sensitive dependence of the largest amplitudes of both fields (which correspond with the tail of the distribution) on the spectral resolution. The probability density functions of each single field as well as their joint distribution vary significantly with increasing distance from the wall. The largest fluctuations of the velocity gradients are found in the logarithmic layer. This is in agreement with recent experiments which observe a bursting of hairpin vortex packets into the logarithmic region. 相似文献
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Kim JY 《The Journal of the Acoustical Society of America》2003,113(5):2442-2445
A self-consistent method for analyzing antiplane shear wave propagation in two-dimensional inhomogeneous media is presented. For applications in the high-frequency range, the self-consistent condition for the effective medium is solved being supplemented with the theory of quasidynamic effective density. Comparisons with other theoretical calculations and experimental data for fiber-reinforced composites demonstrate the merits of using the present method. 相似文献
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Jacob X Catheline S Gennisson JL Barrière C Royer D Fink M 《The Journal of the Acoustical Society of America》2007,122(4):1917-1926
This paper describes nonlinear shear wave experiments conducted in soft solids with transient elastography technique. The nonlinear solutions that theoretically account for plane and nonplane shear wave propagation are compared with experimental results. It is observed that the cubic nonlinearity implied in high amplitude transverse waves at f(0)=100 Hz results in the generation of odd harmonics 3f(0), 5f(0). In the case of the nonlinear interaction between two transverse waves at frequencies f(1) and f(2), the resulting harmonics are f(i)+/-2f(j)(i,j=1,2). Experimental data are compared to numerical solutions of the modified Burgers equation, allowing an estimation of the nonlinear parameter relative to shear waves. The definition of this combination of elastic moduli (up to fourth order) can be obtained using an energy development adapted to soft solid. In the more complex situation of nonplane shear waves, the quadratic nonlinearity gives rise to more usual harmonics, at sum and difference frequencies, f(i)+/-f(j). All components of the field have to be taken into account. 相似文献
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The paper describes a method of exciting a shock wave in a T-shaped discharge tube. It gives the results of measuring the rate of propagation of a shock wave in air, helium and krypton in a pressure range of 10–2 – 1 tor. It also gives the oscillograms of the discharge current, voltage and time derivative of the current and calculates some of the characteristic properties of the circuit, part of which is the exciting discharge.In conclusion the authors would like to thank Assist. Prof. Kracik for his help. 相似文献
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理论上分析了超声光栅衍射和液体表面波光栅衍射,得到了表面波光栅衍射图样与表面波参数的解析关系.实验上得到清晰的衍射图样,利用表面波光栅衍射法测量了液体表面波波速,实验结果与理论值误差不超过1%. 相似文献
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《Physics letters. A》1997,236(3):223-226
The parallel velocity shear instability (PVSI) is experimentally investigated in a double-ended Q machine in which the shear in the ion flow is produced by suitable shaping of the axial magnetic field. Instability fluctuation levels approaching nearly 100% are often observed. 相似文献
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Recently developed continuum mixture theories are extended to study the propagation of horizontally polarized shear waves in a trilaminated wave guide. A specific composite model is considered which resembles the case in which one of the materials acts as a bonding agent for the other two materials. Dispersion relations are derived and compared with exact predictions. Good correlation is shown for significant frequency ranges, especially for the lowest two modes. 相似文献
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The dependencies of phase velocity and dispersion on trabecular thickness and spacing in trabecular bone-mimicking phantoms 总被引:4,自引:0,他引:4
Wear KA 《The Journal of the Acoustical Society of America》2005,118(2):1186-1192
Frequency-dependent phase velocity was measured in trabecular-bone-mimicking phantoms consisting of two-dimensional arrays of parallel nylon wires (simulating trabeculae) with thicknesses ranging from 152 to 305 microm and spacings ranging from 700 to 1000 microm. Phase velocity varied approximately linearly with frequency over the range from 400 to 750 kHz. Dispersion was characterized by the slope of a linear least-squares regression fit to phase velocity versus frequency data. The increase in phase velocity (compared with that in water) at 500 kHz was approximately proportional to the (1) square of trabecular thickness, (2) inverse square of trabecular spacing, and (3) volume fraction occupied by nylon wires. The first derivative of phase velocity with respect to frequency was negative and exhibited nonlinear, monotonically decreasing dependencies on trabecular thickness and volume fraction. The dependencies of phase velocity and its first derivative on volume fraction in the phantoms were consistent with those reported in trabecular bone. 相似文献