We present a multiscale modeling approach to study oxygen diffusion in cubic yttria‐stabilized zirconia. In this approach, we employ density functional theory methods to calculate activation energies for oxygen migration in different cation environments. These are used in a kinetic Monte Carlo framework to calculate long‐time oxygen diffusivities. Simulation results show that the oxygen diffusivity attains a maximum value at around 0.1 mole fraction yttria. This variation in the oxygen diffusivity with yttria mole fraction and the calculated values for the diffusivity agree well with experiment. The competing effects of increased oxygen vacancy concentration and increasing activation energy and correlation effects for oxygen diffusion with increasing yttria mole fraction are responsible for the observed dopant content dependence of the oxygen diffusivity. We provide a detailed analysis of cation‐dopant‐induced correlation effects in support of the above explanation.

No abstract

There is clear evidence that species' ranges along environmental gradients are constrained by both biotic and abiotic factors, yet their relative importance in structuring realized distributions remains uncertain. We surveyed breeding bird communities while collecting in situ temperature and vegetation data along five elevational transects in the Himalayas differing in temperature variability, habitat zonation, and bird richness in order to disentangle temperature, habitat, and congeneric competition as mechanisms structuring elevational ranges. Our results from species' abundance models representing these three mechanisms differed markedly from previous, foundational research in the tropics. Contrary to general expectations, we found little evidence for competition as a major determinant of range boundaries, with congeneric species limiting only 12% of ranges. Instead, temperature and habitat were found to structure the majority of species' distributions, limiting 48 and 40% of ranges, respectively. Our results suggest that different mechanisms may structure species ranges in the temperate Himalayas compared to tropical systems. Despite recent evidence suggesting temperate species have broader thermal tolerances than tropical species, our findings reinforce the notion that the abiotic environment has significant control over the distributions of temperate species.

A nonequilibrium stage model is developed for the simulation of countercurrent multicomponent separation processes. A feature of the model is that the component material and energy balance relations for each phase together with mass and energy transfer rate equations and equilibrium equations for the phase interface are solved to find the actual separation directly. Computations of stage efficiencies are entirely avoided. A procedure for solving the model equations simultaneously using Newton's method is outlined.