Modeling of pair distribution functions for XAFS in disordered systems

A commonly used expression for modeling the XAFS of highly disordered systems is shown to generate substantial systematic errors in the coordination number in many cases of practical interest. This expression is corrected and generalized. Further, a simpler and more flexible model distribution is proposed, and the corresponding XAFS expression is derived. Comparison with experimental and simulated data show that the new expressions are useful in cases of high disorder for which the cumulant expansion loses its utility, and they explicitly account for the k-dependence of the mean free path.     

The stability of metallic glasses under ion irradiation

Abstract

Metallic glasses of Fe₈₀B₂₀ and Fe₈₀P₁₃C₇ prepared by rapid quenching have been implanted with 40 keV Ar⁺, P⁺ and B⁺ ions at doses up to 2.10¹⁶ ions cm^?2 at 273 K. The structure of the glasses was examined by X-ray diffraction. Crystallites of α-Fe and Fe₃B, present in F₈₀B₂₀ samples, either become highly defective or are amorphised. Implantation also produces structural changes in the amorphous Fe₈₀B₂₀ (a-Fe₈₀B₂₀) phase as revealed by changes in the width β of the principal diffraction halo. Both disordering and relaxation effects are observed, dependent on the initial degree of order within the a-Fe₈₀B₂₀ phase before irradiation. Implantation of F₈₀p₁₃C₇ results in an increase in the content of γ-Fe and Fe₃P crystallites, already present before irradiation, and in the nucleation of α-Fe.     

Development of a trace gas stable isotope capture system in a mobile laboratory for temporal and spatial sampling of field and laboratory experiments

We describe the development of a novel mobile field laboratory, purposely designed for the automated capture and subsequent stable isotopic analyses of multiple gas samples. The multiple capture system is integrated into a mobile laboratory that is fully capable of measuring the concentration of carbon dioxide, methane and nitrous oxide trace gases in a flow-through system connected to a gas chromatograph fitted with both electron capture and flame ionisation detectors. The capture of gases is achieved by routing samples through a series of 135 mL gas flasks that are sealed by micro-solenoid valves triggered by a timing system. Trace gas light stable isotope ratio mass spectrometry can then be carried out on gas samples collected by the system (NERC (15)N Stable Isotope Facility). The excitingly unique potential of the system to the ecological research field is that it will allow the collection of cyclical data for three different trace gases both in real-time and in situ. We present data arising from the validation of this mobile system as well as a preliminary experimental assessment of this technique. This technique was used to measure delta(13)C in CO(2) and CH(4) in soil gases released from waterlogged cores and delta(13)C-CH(4) values were significantly depleted in wet cores compared with dry ones (p < 0.001).     

Selective hydrolysis of peptides promoted by metal ions: a positional scanning approach

Rapid, microplate-based fluorogenic screening of a positional scanning combinatorial library accurately predicts the sequence specificity of metal-assisted peptide hydrolysis.     

Polar,non-coordinating ionic liquids as solvents for the alternating copolymerization of styrene and CO catalyzed by cationic palladium catalysts

The palladium-catalyzed copolymerization of styrene and CO in an ionic liquid solvent, 1-hexylpyridinium bis(trifluoromethanesulfonyl)imide, gave improved yields and increased molecular weights compared to polymerizations run in methanol.     

Modeling elasticity in crystal growth

A new model of crystal growth is presented that describes the phenomena on atomic length and diffusive time scales. The former incorporates elastic and plastic deformation in a natural manner, and the latter enables access to time scales much larger than conventional atomic methods. The model is shown to be consistent with the predictions of Read and Shockley for grain boundary energy, and Matthews and Blakeslee for misfit dislocations in epitaxial growth.