Diffusion mechanism in the sodium-ion battery material sodium cobaltate

High performance batteries based on the movement of Li ions in Li_xCoO₂ have made possible a revolution in mobile electronic technology, from laptops to mobile phones. However, the scarcity of Li and the demand for energy storage for renewables has led to intense interest in Na-ion batteries, including structurally-related Na_xCoO₂. Here we have determined the diffusion mechanism for Na_0.8CoO₂ using diffuse x-ray scattering, quasi-elastic neutron scattering and ab-initio molecular dynamics simulations, and we find that the sodium ordering provides diffusion pathways and governs the diffusion rate. Above T ~ 290 K the so-called partially disordered stripe superstructure provides channels for quasi-1D diffusion, and melting of the sodium ordering leads to 2D superionic diffusion above T ~ 370 K. We obtain quantitative agreement between our microscopic study of the hopping mechanism and bulk self-diffusion measurements. Our approach can be applied widely to other Na- or Li-ion battery materials.

Compensatory dynamics are rare in natural ecological communities

In population ecology, there has been a fundamental controversy about the relative importance of competition-driven (density-dependent) population regulation vs. abiotic influences such as temperature and precipitation. The same issue arises at the community level; are population sizes driven primarily by changes in the abundances of cooccurring competitors (i.e., compensatory dynamics), or do most species have a common response to environmental factors? Competitive interactions have had a central place in ecological theory, dating back to Gleason, Volterra, Hutchison and MacArthur, and, more recently, Hubbell's influential unified neutral theory of biodiversity and biogeography. If competitive interactions are important in driving year-to-year fluctuations in abundance, then changes in the abundance of one species should generally be accompanied by compensatory changes in the abundances of others. Thus, one necessary consequence of strong compensatory forces is that, on average, species within communities will covary negatively. Here we use measures of community covariance to assess the prevalence of negative covariance in 41 natural communities comprising different taxa at a range of spatial scales. We found that species in natural communities tended to covary positively rather than negatively, the opposite of what would be expected if compensatory dynamics were important. These findings suggest that abiotic factors such as temperature and precipitation are more important than competitive interactions in driving year-to-year fluctuations in species abundance within communities.

A non-aversive rehabilitation approach for people with severe behavioural problems resulting from brain injury

An approach is presented which uses exclusively non-aversive methods in the behavioural rehabilitation of people with severe behaviour problems resulting from acquired brain injury. The approach has five components: (1) behavioural assessment: analysing the way all aspects of a person's functioning may affect their behaviour, (2) positive programming: teaching the skills necessary to allow the person to achieve their desired ends without resorting to inappropriate behaviour, (3) ecological change: altering the environment to achieve a better match with the individual's cognitive deficits, (4) focused treatment: using behavioural contingencies to achieve a rapid reduction in target behaviour, and (5) reactive strategies: specifying action to be taken to gain short-term control over episodes of challenging behaviour. The current literature on behavioural rehabilitation is reviewed in the context of this approach. Two case studies are presented illustrating the use of the approach in practice. The strengths and potential pitfalls of the approach are discussed, along with issues which need to be considered for effective implementation.