The acoustic nonlinearity parameter, B/A, is an important parameter which defines the way a propagating finite amplitude acoustic wave progressively distorts when travelling through any medium. One measurement technique used to determine its value is the finite amplitude insertion substitution (FAIS) method which has been applied to a range of liquid, tissue and tissue-like media. Importantly, in terms of the achievable measurement uncertainties, it is a relative technique. This paper presents a detailed study of the method, employing a number of novel features. The first of these is the use of a large area membrane hydrophone (30 mm aperture) which is used to record the plane-wave component of the acoustic field. This reduces the influence of diffraction on measurements, enabling studies to be carried out within the transducer near-field, with the interrogating transducer, test cell and detector positioned close to one another, an attribute which assists in controlling errors arising from nonlinear distortion in any intervening water path. The second feature is the development of a model which estimates the influence of finite-amplitude distortion as the acoustic wave travels from the rear surface of the test cell to the detector. It is demonstrated that this can lead to a significant systematic error in B/A measurement whose magnitude and direction depends on the acoustic property contrast between the test material and the water-filled equivalent cell. Good qualitative agreement between the model and experiment is reported. B/A measurements are reported undertaken at (20 ± 0.5) °C for two fluids commonly employed as reference materials within the technical literature: Corn Oil and Ethylene Glycol. Samples of an IEC standardised agar-based tissue-mimicking material were also measured. A systematic assessment of measurement uncertainties is presented giving expanded uncertainties in the range ±7% to ±14%, expressed at a confidence level close to 95%, dependent on specimen details.

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The electronic specific heat coefficient, y, the Debye temperature, OD, and the superconducting transition temperature, T,, have been measured for binary b.c.c. alloys of V, Nb, and Ta. These results have been used to investigate the effects of compositional changes on parameters used in the theory of superconductivity to describe the transition temperature. It has been shown that changes in transition temperature with changes in composition cannot be explained simply on the basis of an alteration of the density of states except in the case of binary Nb-Ta alloys. It is concluded that, for V-Nb and V-Ta alloys, changes in the interaction responsible for superconductivity also govern changes in the transition temperature.La coefficient du chaleur specifique Blectronique, y, la t e m p h t u r e de Debye, OD, et la temperature de transition supraconductrice, T,, ont BtB dBterminBs pour des alliages binaires dc type cubique centre et qui contiennent V, Nb et Ta. L'on a utilise ces resultats afin d'Btudier l'influence de composition sur des paramhtres ceux qui expliquent la tempbrature de transition dans la t,heorie de supraconductivith. L'on ne peut pas expliquer la variation dans la tempbrature de transition en fonction de la composition par le changement de la densitk; d'htats, sauf pour lea alliages Nb-Ta. L'on concluit que pour des alliages V-Nb et V-Ta, des variations dans l'interaction responsible pour la supraconductivit6 dbterminent des variations dans la t e m p h t u r e de transition.

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