In-situ identification of iron--zinc intermetallics in galvannealed steel coatings and iron oxides on exposed steel

Identification of all the compounds present in various coatings on steels is particularly difficult. Non-destructive, in-situ analysis is necessary if the fraction of each compound as well as its probable layering within the coating, is to be determined. Mössbauer spectroscopy is one valuable probe capable of uniquely identifying all iron compounds which form as coatings on steel and other iron alloy surfaces. To investigate a complete coating several criteria need to be considered. Removing the coating inevitably leaves a small and perhaps important component intact on the substrate. Therefore investigating the coating as it remains intact on the steel is important if complete identification of the iron compounds is to be made. This also preserves crystalline texture or preferred growth orientation within the coating to which the Mössbauer effect is sensitive. Mössbauer spectroscopy is a non-destructive technique which allows the integrity of the coating to be maintained during analysis. The combined transmission and scattering Mössbauer geometries generally result in accurate analysis of the coating composition. For the scattering geometry added information on compound layering is obtained if separate Mössbauer spectra are recorded using the re-emitted gamma rays as well as the conversion electrons and subsequently emitted X-rays. In-situ scattering Mössbauer spectroscopy has been used to characterize the iron--zinc alloys which form in the coatings of commercially produced corrosion resistant galvannealed sheet steel, a product of great interest to automotive producers. The results show that different amounts of four iron--zinc phases are present depending on the production conditions of the coating. The different phases are also distinctly layered. Mössbauer analyses of corrosion coatings formed on the surface of steels which have been exposed to different environments has also been undertaken. Materials include structural steels exposed for up to 25 years in marine, rural and industrial environments, and the interior surfaces of boiler pipes subjected to adverse chemical and temperature environments.     

Runge-Kutta stability on a Floquet problem

This work examines the stability of explicit Runge-Kutta methods applied to a certain linear ordinary differential equation with periodic coefficients. On this problem naïve use of the eigenvalues of the Jacobian results in misleading conclusions about stable behaviour. It is shown, however, that a valid analogue of the classical absolute stability theory can be developed. Further, using a suitable generalisation of the equilibrium theory of Hall [ACM Trans. on Math. Soft. 11 (1985), pp. 289–301], accurate predictions are made about the performance of modern, adaptive algorithms.Supported by the University of Dundee Research Initiatives Fund.     

Amorphous BeN as a new solid host for rare‐earth‐related luminescent materials

Beryllium‐nitride (BeN) thin films were prepared by sputtering a Be target in an atmosphere of pure nitrogen. The films were doped with samarium simply by placing a piece of Sm metal on the surface of the Be target. Under these deposition conditions the films present an amorphous structure and an optical bandgap of approx. 4 eV. They also exhibit visible light emission due to Sm³⁺ ions as a result of either photon or electron excitation. The present experimental results show that amorphous BeN films are suitable, and efficient, III‐nitride hosts for rare‐earth doping purposes. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Speaking rate of adventitiously deaf male cochlear implant candidates

No objective group data on speaking rate or speaking duration have been reported on the speech of adventitiously profoundly hearing-impaired adults. Results of the present study showed that speaking rate, i.e., number of syllables per second, was significantly slower and speaking duration was significantly longer for 25 adventitiously profoundly hearing-impaired adult male cochlear implant candidates than for 10 normal-hearing control subjects. The factors of length of time since onset of profound hearing loss and hearing aid use did not significantly affect speaking rate. Based on these objective data, a rationale and method are presented for aural rehabilitation of the profoundly hearing-impaired who exhibit speaking rate abnormalities.     

Effects of bleaching on the sensitivity to dose of the infrared-stimulated luminescence of potassium-rich feldspars from Ynyslas, Wales

Reduction of the luminescence signal to a residual level before irradiation is an inherent part of the regeneration method of equivalent dose (ED) determination, but is likely to lead to changes in the sensitivity of the dosimeter. Sensitivity changes caused by different methods of reduction of the infrared- stimulated luminescence (IRSL) signal have been investigated by subjecting potassium-rich feldspars extracted from modern dune sand from Ynyslas, on the Dyfi Estuary in Wales, to repeated cycles of removal of the luminescence signal and beta irradiation. The methods used to remove the signal were exposure to natural sunlight, a solar simulator and infrared-emitting diodes with a wavelength of 880Δ 80 nm and heating to 450°C.     

Comparative extreme ultraviolet emission measurements for lithium and tin laser plasmas

Detailed spectroscopic studies on extreme UV emission from laser plasmas using tin and lithium planar solid targets were completed. At 13.5 nm, the best conversion efficiency (CE) for lithium was found to be 2.2% at intensities near 7 x 10(10) W/cm(2). The highest CE measured for tin was near 5.0% at an intensity close to 1 x 10(11) W/cm(2).     

Freezing-off in disc cavities

A semi-quantitative analysis is presented of freezing-off in a disc cavity during the injection moulding of thermoplastics. A criterion is obtained which enables the occurrence of freezing-off to be predicted, at least crudely. The form of the criterion is found to depend on the direction of flow (radially outward or inward) in the disc.     

Injection moulding of thermoplastics. I. Freezing-off at gates

The injection moulding of thermoplastics involves, during mould filling, flow of a hot molten polymer into a mould network, the walls of which are so cold that the polymer freezes on them. During the constant pressure drop part of the filling stage, but not during the preceding constant flow-rate part, freezing-off, that is premature blockage of the mould network by frozen polymer, is possible. A semi-quantitative analysis of such freezing-off at a gate is presented here. The length-scales and time-scales of all the relevant physical processes occurring during freezing-off are identified and a criterion is obtained which enables the occurrence of freezing-off to be predicted, at least crudely. a _j constant - b _jk constant - Br Brinkman number - Br ₀ initial Brinkman number - Gz Graetz number - Gz ₀ initial Graetz number - h _c half-height of flat cavity - h _g half-height of flat gate - h _g ^* half-height of polymer melt region in flat gate - L _c length of cavity - L _f filled length - L _g length of gate - m viscosity shear-rate exponent - P pressure drop - Q volumetric flow-rate - r radial coordinate in round gate and cavity - R _c radius of round cavity - R _g radius of round gate - R _g ^* radius of polymer melt region in round gate - Sf Stefan number - t time - t _f freeze-off time - T temperature - T _i inlet polymer melt temperature - T _m melting temperature of polymer - T _w gate wall temperature - u _r radial velocity in round gate - u _x axial velocity in flat gate - u _y transverse velocity in flat gate - u _z axial velocity in round gate - w _c width of flat channel - w _g width of flat gate - x axial coordinate in flat gate and cavity - y transverse coordinate in flat gate and cavity - z axial coordinate in round gate and cavity - thermal conductivity of molten polymer - thermal conductivity of frozen polymer - heat capacity of molten polymer - heat capacity of frozen polymer - _h ratio of half-height of flat gate to that of flat cavity - _R ratio of radius of round gate to that of round cavity - _w ratio of width of flat gate to that of flat cavity - dimensionless axial coordinate in round gate and cavity - dimensionless transverse coordinate in flat gate and cavity - ^* dimensionless half-height of polymer melt region in flat gate - dimensionless temperature - _i dimensionless inlet temperature - _j j-th term in power series expansion of dimensionless temperature - thermal diffusivity ratio - dimensionless filled length - latent heat of fusion of polymer - µ viscosity - µ ₀ unit shear-rate viscosity - v _j j-th eigenvalue - j-th zero of zeroth-order Bessel function of first kind - dimensionless axial coordinate in flat gate and cavity - _c dimensionless pressure drop in cavity - _g dimensionless pressure drop in gate - density of molten polymer - density of frozen polymer - dimensionless radial coordinate in round gate and cavity - ^* dimensionless radius of polymer melt region in round gate - dimensionless time - _f dimensionless freeze-off time - ₀ dimensionless time at start of final phase of freezing-off - rescaled dimensionless time - rescaled dimensionless freeze-off time - rescaled dimensionless time at start of final phase of freezing-off - dimensionless similarity variable - dummy variable - scaled dimensionless axial coordinate in gate     

Influence of Ag+ on the Magnetic Response of [2.2.2]Paracyclophane: NMR Properties of a Prototypical Organic Host for Cation Binding Based on DFT Calculations

The complexation of metal cations into a host–guest situation is particularly well exemplified by [2.2.2]paracyclophane and Ag^I, which leads to a strong cation–π interaction with a specific face of the host molecule. Through this study we sought a deeper understanding of the effects the metal center has on the NMR spectroscopic properties of the prototypical organic host, generating theoretical reasons for the observed experimental results with an aim to determine the role of the cation–π interaction in a host–guest scenario. From an analysis of certain components of the induced magnetic field and the ¹³C NMR shielding tensor under its own principal axis system (PAS), the local and overall magnetic behavior can be clearly described. Interestingly, the magnetic response of such a complex exhibits a large axis-dependent behavior, which leads to an overall shielding effect for the coordinating carbon atoms and a deshielding effect for the respective uncoordinated counterparts, evidence that complements previous experimental results. This proposed approach can be useful to gain further insight into the local and overall variation of NMR shifts for host–guest pairs involving both inorganic and organic hosts.