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    ABSTRACT: This paper presents time resolved quantitative evaluation of elastic stress waves in solid media by utilising an adaptation of the well-established laser Doppler vibrometry method. We show that the introduction of elastic stress waves in a transparent medium gives rise to detectable and quantifiable changes in the refractive index, which is proportional to stress. The method is tested for mechanical excitation at frequencies from 10 to 25 kHz in an acrylic bar. This refractometric quantification can measure internal strains as low as 1 × 10−11. Additionally, finite element analysis is conducted to gauge the validity of the results. In the presented work an acrylic bar is used, this method however should be applicable to any transparent solid.
    Measurement 09/2014; 55:51–57. DOI:10.1016/j.measurement.2014.04.038
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    ABSTRACT: In this work the initial stages of oxidation of a uranium-base alloy (U -6 wt.% Nb) during exposure to a UHV environment consisting primarily of H 2 O, CO and CO 2 have been studied using the specific surface analysis technique of angled resolved X-ray photoelectron spectroscopy (ARXPS). Examination of the sputter cleaned surface of the alloy has been performed at different take-off angles varying between 0° and 60° prior to and after a prolonged exposure to the UHV atmosphere for approximately 2 hours. The photoelectron spectra recorded for U 4f, Nb 3d and O 1s indicated that the adsorption and dissociation of H 2 O, CO and CO 2 on the alloy surface first leads to the formation of UO 2 intermixed with NbO. Other oxides including NbO 2 and Nb 2 O 5 along with hydroxyl compounds were clearly detected after exposure times exceeding one hour (360 L). The formation of a critical density of Nb 2 O 5 at the metal-oxide interface is suggested to play a key role in preventing the diffusion of ionic species such as O -and OH – into the oxide-metal interface region, thus conferring a much higher resistance to oxidation and corrosion on the alloy, as compared with that of the unalloyed uranium metal.
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