Recent research using the Oxford electron beam ion trap

The presence of the σ-phase in Fe-Cr alloys (eg. Stainless steel) is important in industrial applications and from an academic point of view. The presence of the σ-phase in these alloys drastically affects their mechanical properties and their resistance to various corrosive media. In the present investigation Fe-Cr alloys containing different amounts of Mo were prepared and the transformation to the σ-phase was carried out by isothermally annealing the samples for various periods in an argon atmosphere. It will be shown that the presence of Mo has a dramatic accelerating effect on the rate of the σ-phase formation in these alloys. This revised version was published online in August 2006 with corrections to the Cover Date.     

Absolute rate constants for reactions of free radicals in the high-temperature photolysis of formamide vapor. II. Amino radicals

The rotating-sector method has been applied to the photoinitiated radical-chain decomposition of formamide at 300°C to measure the rate constant for the bimolecular disappearance of NH₂ radicals. The decomposition is propagated by the reactions (1) (2) Conditions were chosen so that reaction (1) was rate controlling and NH₂ the terminating radical. A flow system was employed with C₂F₆ as a carrier gas at a pressure of 300 Tort, and the chain reaction was initiated by the photolysis of either formamide or NH₃. A value of 4.7(±2.0) × 10¹⁰ (M ·sec)^?1 was estimated for the termination reaction (3) and a value of 8.4 × 10⁶ (M ·sec)^?1 for reaction (1) in the same system, both at 300°C.     

Rate constants for abstraction of hydrogen from ethylene by methyl and ethyl radicals relative to abstraction from propane and isobutane

A method is described for the measurement of relative rate constants for abstraction of hydrogen from ethylene at temperatures in the region of 750 K. The method is based on the effect of the addition of small quantities of propane and isobutane on the rates of formation of products in the thermal chain reactions of ethylene. On the assumption that methane and ethane are formed by the following reactions, (1) measurements of the ratio of the rates of formation of methane and ethane in the presence and absence of the additive gave the following results: Values for k₂ and k₃ obtained from these ratios are compared with previous measurements.     

Fission induced by heavy-ion collisions

Fission fragment angular distributions from sequential fission induced in heavy-ion reactions will depend on the angular momentum exchange occuring in such reactions in considerable detail. Theoretical expressions for the angular distributions of fission products from totally and partly polarized nuclei are presented. They are compared with recent measurements and discussed in relation to the deep inelastic reaction mechanism.     

Stage effects of negative emotion on spatial and verbal working memory

Background  

The effects of negative emotion on different processing periods in spatial and verbal working memory (WM) and the possible brain mechanism of the interaction between negative emotion and WM were explored using a high-time resolution event-related potential (ERP) technique and time-locked delayed matching-to-sample task (DMST).     

Spatially resolved dynamic eigenmode spectrum of Co rings

The spatially resolved eigenmode spectrum of micrometer-sized Co ring elements has been determined by means of combined vector network analyzer ferromagnetic resonance and time resolved magneto-optic Kerr effect measurements. Up to 5 resonant eigenmodes were observed in the frequency range from 45 MHz to 20 GHz as a function of an external magnetic bias field. A well-defined mode structure was found for the two equilibrium states (vortex and onion) which correspond to distinctive spatial modes. The effect of dynamic inter-ring coupling on the modes in the remanent states was evinced. The experimental results are found to be in good agreement with those of micromagnetic simulations. Our results demonstrate that, in analogy to the well-defined static equilibrium magnetic states of ring elements, the eigenmode spectra of this high symmetry geometry consist of a well-defined and simple mode structure.     

‘It takes me longer,but I understand better’ – student feedback on structured derivations

In this article, we present the results from a qualitative study on students' initial reactions to the use of structured derivations in mathematics education. Our findings suggest that the approach increases the clarity of solutions and facilitates debugging of proofs. It also has potential to increase students' self-perceived level of understanding. Our findings indicate that the main drawbacks experienced by the students are related to time and length. Nevertheless, the overall feedback on the approach was found to be positive, thus encouraging further use of structured derivations in mathematics education.     

Key steps and intermediates in the catalytic mechanism for the reduction of peroxides by the antioxidant ebselen

Hydrogen peroxide and lipid hydroperoxides are formed during aerobic metabolism and contribute to oxidative stress, a major factor in many diseases and degenerative conditions. Although the selenoenzyme glutathione peroxidase (GPx) affords antioxidant protection in vivo by catalytically reducing harmful peroxides with glutathione, certain conditions benefit from the administration of small-molecule GPx mimetics for additional protection. To date, ebselen has been the most widely studied such compound, but its catalytic mechanism is complex and highly variable with conditions. Progress in elucidating the mechanistic details of its antioxidant activity is described in this review.     

1,3-Dipolar cycloadditions of acetylenic sulfones in solution and on solid supports

Several representative acetylenic sulfones were immobilized on a polymer support derived from Merrifield resin by means of ester linkers that were used to couple free carboxylic acid groups on the solid support with benzylic hydroxyl functions on the arylsulfonyl moieties of the acetylenes. Several examples of reversed ester linkers, using Merrifield resin directly, were also successfully prepared. The 1,3-dipolar cycloadditions of the solid-supported acetylenic sulfones were investigated with a series of 1,3-dipoles, including benzyl azide, ethyl diazoacetate, diazomethane, as well as representative nitrile oxides, nitrile imines, nitrile ylides, nitrones, azomethine imines, azomethine ylides, munchnones, and sydnones. In general, analogous cycloadditions were also performed with acetylenic sulfones in solution phase for comparison. The cycloadditions typically afforded good to excellent yields of the desired products in both solution and solid phase, although the latter reactions sometimes required more vigorous conditions. Except in the case of benzyl azide and diazo compounds, where mixtures of regioisomers were obtained, the other 1,3-dipoles reacted with high regioselectivity and afforded essentially unique regioisomers. Cleavage of the products from the resin was smoothly effected by alkaline hydrolysis, while several attempts at reductive desulfonylation with sodium amalgam or samarium diiodide-HMPA resulted in N-O or C-O scission, in addition to cleavage from the polymer. The method provides access to a number of important classes of heterocycles, including variously substituted and functionalized triazoles, pyrazoles, 1,2-oxazoles, pyrroles, as well as their dihydro and bicyclic analogues. The success of the cycloadditions on polymer supports paves the way to future investigations of sequential transformations leading to libraries of useful heterocycles.