Showing papers in "Ultrasonics in 1987"

TL;DR: In this article, the chemical effects of pulsed ultrasound are described and discussed with respect to the use of ultrasonic pulses in medical diagnosis, and the results of these reactions are discussed.

TL;DR: In this article, the mechanism of metal solidification in an ultrasonic field and associated structure changes in ingots is described, and the effects of material properties and solidification conditions on the effectiveness of structure refinement during ultrasonic treatment are evaluated.

TL;DR: Scanning electron microscopy reveals that ultrasound has multiple effects on the morphology and surface characteristics of inorganic solids, creating substantial surface damage, increasing surface areas significantly and causing increased particle aggregation.

TL;DR: In this article, it was shown that due to the formation of standing waves, the local ultrasound intensity in a flask fixed in an ultrasonic cleaner is strongly susceptible to small changes in experimental conditions.

TL;DR: In this paper, preliminary results support the view that the presence of oxygen in a cavitating liquid generates singlet oxygen in addition to peroxy radicals, which can be used in several phase transfer catalysed reactions, e.g. Nalkylation of amines, synthesis of ethers and esters and hydrolysis of esters.

TL;DR: In this article, the angular dependences of the long wavelength velocities of S0 and SH0 modes of orthorhombic (orthotropic) plates are compared to those of the velocity of corresponding plane waves.

TL;DR: In this paper, the relative performance of several types of ultrasonic transducers are assessed using reproducible acoustic transients generated from Q-switched Nd:YAG laser pulses incident on an aluminium alloy sample.

TL;DR: In this article, the Ullmann coupling reaction of 2-iodonitrobenzene in the presence of a four-fold excess of copper in DMF was investigated and decalin or toluene was found to lead to substantial reductions in reaction rate.

TL;DR: In this article, the authors provide experimental confirmation of a recently postulated procedure for optimizing the choice of processing parameters in split spectrum processing and demonstrate its application to signal-to-noise ratio enhancement in welds, centrifugally cast stainless steel and carbon-epoxy composites.

TL;DR: In this paper, the authors consider quantitative acoustic emission (AE) techniques with real and simulated sources as powerful tools for investigating failure processes in composite materials using a simulated source acting as a point source and one or more point receivers whose characteristics are known.

TL;DR: This work has detected free radicals in aqueous solutions exposed to microsecond pulsed ultrasound using spin trapping and electron spin resonance (ESR).

TL;DR: Comparison between the results obtained from the three techniques shows that: if only echography provides a real-time acquisition of signals, tomographic methods lead to faster processing associated with a better signal-to-noise ratio on the reconstructed images, and reflection tomography offers the best definition.

TL;DR: To obtain a good dynamic range on echographic signals produced by broad-band piezoelectric arrays with frequencies > 4 MHz, it is necessary to excite each of the array elements with very fast electric spikes as mentioned in this paper.

TL;DR: In this paper, a region of maximum structure in the binary mixture of 2-chloro-2-methylpropane and 2-methyl-propane in aqueous ethanol mixtures was found to acclerate the solvolysis.

TL;DR: In this article, the effects of polymers on cavitation damage and noise spectra were evaluated in a polymer solution and water, and the results showed that cavitation noise in the high frequency range in the polymer solution was large compared to those obtained in water.

TL;DR: In this paper, the authors compare the properties of the well known synthetic aperture focusing technique (SAFT) with those of two deconvolution methods, which have previously been less widely applied to digitized ultrasonic data.

TL;DR: The effect of ultrasonic waves on the activity of glucoamylase bound to a porous polystyrene matrix is investigated and the activity increase is discussed in terms of a possible ultrasonic mechanism.

TL;DR: In this article, two signal processing techniques are developed to improve the signal-to-noise ratio in the testing of coarse-grained materials: space minimization-frequency minimization (SMFM) and space minimisation-frequency threshold (SMFT) algorithms.

TL;DR: In this paper, a computer-controlled, fully-automated instrument which measures ultrasound velocities in planar materials is presented, which can completely characterize the in-plane elastic properties of an orthotropic sheet even though it is specifically designed to analyse paper and paperboard samples, other sheet materials can also be tested

TL;DR: In this article, the influence of wear plate and coupling layer thickness on the measurement of ultrasonic velocity using commercially available highly damped transducers has been investigated using a pulse superposition method on samples of duraluminum and steel, and the phase shift, γ, arising between successive echoes from the reflection on the transducer-bond interfaces is calculated from a model that takes into account the presence of the wearplate of the transducers.

TL;DR: In this article, the types of chemical reactions which take place in organic liquids on irradiation with intense ultrasound are reviewed and conditions under which such reactions take place, especially those leading to initiation of polymerization.

TL;DR: In this article, a review summarizes a part of the work undertaken by a group in Grenoble in the area of organometallic sonochemistry and discusses tentative interpretations of the ultrasonic effects on such reactive systems.

TL;DR: The principal ultrasonic parameters which can be measured are the velocity, attenuation and scattering of ultrasound and the acoustic impedance of the medium through which it is travelling as discussed by the authors, from these it is possible to determine, under favourable circumstances, chemical identity, the concentrations (or density) of solutions, mixtures and dispersions, and the particle size of dispersed phases.

TL;DR: The results obtained indicate that the composition and water content of the liver tissue but not its structure determine the value of velocity.

TL;DR: In this article, ultrasonic Rayleigh waves are modelled numerically using explicit finite difference methods, which are part of a group of computer models named USWAPS (Ultra Sonic WAve Propagation and Scattering), are used to study the various geometries of interest.

TL;DR: In this article, the velocity difference of Rayleigh waves propagating along the principal axes of texture and the birefringence of shear waves propagated in the thickness direction is derived for propagation on polycrystalline metal plates with weakly orthorhombic anisotropy modelling the rolling texture.

TL;DR: In this paper, the plane and edge wave model of the action of an ultrasonic transducer was used to predict that improved short-pulse, wideband transducers could be produced by varying the excitation of the transducers elements as a function of the distance from its centre.

TL;DR: By analysing a one-dimensional model for a plaque deposit on the wall of a carotid artery embedded in a 5 cm thick layer of tissue, it is demonstrated that a relatively high quality image can be recovered when compensation for the attenuation of the intervening tissue is made.

TL;DR: The implemented system, which employs bi-phase modulation of the transmitter waveforms with m-sequences and Golay codes, provides significant signal-to-noise ratio enhancement with zero range sidelobes and confirms the feasibility of the method.

TL;DR: In this paper, the authors derived the parameters describing the range and the nature of phase errors in the directivity pattern of a two-dimensional ultrasound system and used these parameters to predict the spatial resolution of a given phased array.