Concerted and stepwise proton-coupled electron transfers in aquo/hydroxo complex couples in water: oxidative electrochemistry of [Os(II)(bpy)(2)(py)(OH(2))](2+)

Successive oxidation of transition metal(II) aqua complexes (M(II)OH(2) to M(III)OH) is a domain in which proton-coupled electron transfer reactions are extremely common. The mechanism of these PCET reactions-concerted or stepwise-is an important issue in the understanding and design of natural or artificial systems catalyzing the formation of dioxygen by four-electron oxidation of water. Concerted proton-coupled electron transfer from an aqua metal(II) to a hydroxo metal(III) complex requires the close proximity of a proton-accepting group with a pK value between those of the aqua complexes. Otherwise, stepwise electron-proton or proton-electron pathways involving high-energy intermediates are followed. Concerted proton-electron pathways involving water as proton-acceptor or proton-donor group are inefficient. Cyclic voltammetry of the title complex in buffered aqueous solution and re-examination of previous results for the same complex attached to an electrode surface are used to establish these conclusions, which provide a starting point on the route to higher degrees of oxidation, such as those involved in the catalysis of water oxidation.     

Exponential smoothing methods in pension funding

‘Smoothed-market’ methods are used by actuaries,when they value pension plan assets, in order to dampen thevolatility in contribution rates recommended to plan sponsors.A method involving exponential smoothing is considered. Thedynamics of the pension funding process is investigated in thecontext of a simple model where asset gains and losses emergeas a result of random rates of investment return and where thegains and losses are spread. It is shown that smoothing marketvalues up to a point does improve the stability of contributionsbut excessive smoothing is inefficient. It is also shown thatconsideration should be given to the combined effect of theasset valuation and gain and loss adjustment methods. Practicaland efficient combinations of gain/loss spreading periods andasset value smoothing parameters are suggested.     

The numerical integration of relative equilibrium solutions. The nonlinear Schrodinger equation

We analyse different error propagation mechanisms for conservativeand nonconservative time-integrators of nonlinear Schrödingerequations. We use a geometric approach based on interpretingwaves as relative equilibria.     

Use of parabolic reflector to amplify in-air signals generated during impact-echo testing

The impact-echo method is a commonly used nondestructive testing technique for elastic plates in civil engineering. The impact-echo mode corresponds to the frequency at zero group velocity of S(1) Lamb mode. Recent development of the air-coupled impact-echo (ACIE) method introduces the possibility for rapid scanning of large structures and increases the practicality of in situ measurements. However, sensors used in ACIE are susceptible to ambient noise, which complicates in situ ACIE measurements. This letter presents the results of ACIE measurements taken using a parabolic reflector together with standard measurement microphones to increase the signal to noise ratio for ACIE measurements. The signal gain and effects of sensor location with respect to impact location are discussed.     

On age-period-cohort parametric mortality rate projections

An enhanced version of the Lee–Carter modelling approach to mortality forecasting, which has been extended to include an age modulated cohort index in addition to the standard age modulated period index, is described and tested for prediction robustness. Life expectancy and annuity value predictions, at pensioner ages and for various periods are compared, both with and without the age modulated cohort index, for the England & Wales male mortality experience. The simulation of prediction intervals for these indices of interest is discussed in detail.     

Nucleation of lead chromate from homogeneous solution

On the basis of the Christiansen-Nielsen model for nucleation, the nucleus of lead chromate precipitated from homogeneous solution has been found to consist of about five ions. The critical supersaturation values of solutions of lead chromate are dependent upon the method of filtration; however, a change in supersaturation of about 25 % is without effect on the size of the critical nucleus.