Acoustic absorption in aqueous potassium phosphate

Measurements of acoustic absorption and velocity as a function of frequency and concentration in KH₂PO₄–K₂HPO₄ buffers at 4°C and pH 5-7 are reported. The dependence of the observed acoustic relaxation parameters on concentration is consistent with that to be expected from perturbation of a monomer-dimer equilibrium with an equilibrium constant [for 2H₂PO ₄ ^– (H₂PO₄)₂ ^2–] of 0.21 M^–1, a bimolecular rate constant of 5×10⁸ M^–1-sec^–1 and a standard volume change of –5 cm³ mole. The equilibrium constant for H₂PO ₄ ^– + HPO₄ ^2–H₃(PO₄)₂ ^3– is estimated to be 0.7 M^–1.     

Ultrasonic study on binary liquid mixtures between some bromoalkanes and hydrocarbons

Densities and ultrasound velocities for the binary mixtures of 1-bromobutane+benzene and 1,4-dimethylbenzene and of 1-bromopentane+cyclohexane and benzene have been measured at 308.15 K. Adiabatic compressibilities (beta(ad)), and Wada's constants (W) have also been evaluated as a function of composition. The ultrasound velocities decrease, attains a minimum and then increase with increase in mole fractions of hydrocarbons in the binary mixtures except in the case of 1-bromopentane+benzene binary mixtures where the variation is just the reverse. Dependence of adiabatic compressibilities with mole fractions of hydrocarbons is sigmoid. The non-ideal behaviour of the systems studied is explained on the basis of dipole-induced dipole interactions.     

A Practical Application of Ultrasonic Thermal Stress Monitoring in Continuous Welded Rails

A methodology designed to monitor thermally induced loads on continuous welded rails (CWR) is presented. The technique is based on the use of sub-surface longitudinal ultrasonic waves (l.c.r. waves) and, by means of a daily data elaboration, allows to obtain the value of the neutral temperature of the rail as a function of time. From such information an estimation of longitudinal stresses, to be used as a reference, can be derived. The methodology here presented has undergone a 2 years testing period, through the instrumentation of about 3 km of railway track. All acquired data have been remotely processed in a single control station.     

An <Emphasis Type="Italic">In Situ</Emphasis> Ultrasonic Technique for Simultaneous Measurement of Longitudinal and Shear Wave Speeds in Solids

Ultrasonic wave speed measurements are widely used to infer the elastic properties of solids. In the standard method, longitudinal and shear transducers are used separately to measure the corresponding wave speeds in a material. A new experimental method is introduced for simultaneously measuring the longitudinal and the shear wave speeds using a single set of longitudinal or shear transducers. The method can also be used to measure the wave speeds in situ during deformation by placing the transducers along the loading axis. The transducers are housed in a specially designed fixture such that they are not subjected to loading. The technique is demonstrated by performing uniaxial compression experiments on fully dense isotropic solids (where the wave speeds are not expected to change during deformation) and in polymeric foams (where the wave speeds are affected by damage).     

Viscoelastic investigation by ultrasonic shear waves of liquid eutectic mixture methylurea–ammonium sulfamate

Shear impedance of the liquid eutectic mixture CH₃NHCONH₂–NH₄SO₃NH₂ was studied in the temperature range 291.7–313.2 K by using ultrasonic shear waves in the frequency range 12–80 MHz. Ultrasonic technique allowed the determination of the real part of the complex mechanical impedance and of the complex rigidity modulus. The relaxation region was shifted towards higher frequency in comparison to the Maxwell model and was fitted by the modified BEL model.     

柱状分层固体媒质的声散射

本文评述了各向同性和横向各向同性柱状分层固体声散射理论和实验研究进展介绍了描述圆柱状界面薄层特性的弹簧模型，也讨论了该领域中有待进一步研究的一些问题。     

Piezoelectric transducer vibrations in a one-dimensional approximation

Summary The theory of piezoelectric transducer vibrations, which may be treated as onedimensional, is developed in detail for thin discs vibrating in a pure thickness extensional mode. An effort has been made to obtain relations of general validity, which include losses, and which are in a simple explicit form convenient for practical calculations. The behaviour of transducers is discussed with special attention to their characteristics at the two fundamental frequencies, the so-called parallel and series resonances. Several peculiarities occur when transducers are coupled to media with considerably different acoustic impedances. These peculiarities are discussed and illustrated by numerical results for quartz and PZT 4 piezoelectric discs radiating into water, air and liquid hydrogen. The application of the theory to different types of vibrations is briefly illustrated for thin bars vibrating longitudinally. Short discussions are included on compound transducer systems, and on the properties of thin discs as receivers.     

The origin of the redshift in Brillouin spectra of silica films containing tin nanoparticles

The abrupt change of velocity in surface acoustic waves in thin films of amorphous SiO_x containing nanometre scale -Sn crystals is shown to be directly associated with the size-dependent melting of the nanoparticles, confirming preliminary experiments. High resolution thin film powder diffraction using synchrotron radiation shows that the abrupt redshift in the Brillouin spectra satellites occurs at the same temperature as the melting of the nanoparticles, evident for the loss of the Bragg peaks. Effective medium theory is used to explain the origin of the anomaly. A central peak in the Brillouin spectrum, the intensity of which shows a maximum at the melting temperature, can be interpreted in terms of overdamped fluctuations in the dielectric function. The melting temperature as a function of particle size is in agreement with theoretical predictions. No evidence for strain could be found on the X-ray diffraction profiles; the a- and c-axis thermal expansion coefficients are the same as those in bulk tin. Received 30 March 2000 and Received in final form 24 July 2000     

Dislocation density based constitutive model for ultrasonic assisted deformation

The mechanical behaviour of metallic materials subjected to plastic deformation is altered with the superposition of ultrasonic vibrations. A significant effect is the reduction of flow stress or acoustic softening. This phenomenon is utilized in metal forming and other deformation based manufacturing processes. Experimental investigations on ultrasonic assisted tensile tests focus on the effect of ultrasonic vibrations along the longitudinal axis of the specimen, whereas the manufacturing processes employs in transverse directions. In the present work, transverse ultrasonic vibrations are imposed during a uniaxial tensile test using an aluminium alloy. The trend of acoustic softening due to transverse direction vibrations is similar to that along longitudinal direction. A dislocation density based constitutive model is extended to model the softening due to ultrasonic effect. The predicted results agree well with the experimental observations.