Asperity Shape and Gradient Elasticity in Flexoelectric/Triboelectric Contacts

The underlying mechanisms responsible for triboelectricity have yet to be completely understood. We have previously proposed a model which explains charge transfer in non-metals via band bending due to electromechanical, especially flexoelectric, effects at deformed asperities coupled with work function differences. Here, we investigate whether the shape of asperities is important for triboelectricity. The results indicate that the shape is important in general, since how the electromechanical response scales with force and asperity size depends on the shape. This is qualitatively in agreement with experimental results. Further, we discuss how the impact of the shape depends on material, geometric, and electronic transport details. Additionally, gradient elasticity is incorporated into the model. As asperity contact is a nanoscale phenomenon, size-dependent mechanics can become significant and give more physically reasonable results. In some cases, the impact of gradient elasticity terms on the electromechanical potentials is very large, indicating that standard elasticity theory is not enough to cover some relevant cases in modelling triboelectricity.Comment: 21 pages, 11 figure

Profiling the educational value of computer games

There are currently a number of suggestions for educators to include computer games in formal teaching and learning contexts. Educational value is based on claims that games promote the development of complex learning. Very little research, however, has explored what features should be present in a computer game to make it valuable or conducive to learning. We present a list of required features for an educational game to be of value, informed by two studies, which integrated theories of Learning Environments and Learning Styles. A user survey showed that some requirements were typical of games in a particular genre, while other features were present across all genres. The paper concludes with a proposed framework of games and features within and across genres to assist in the design and selection of games for a given educational scenari

Direct Visualization of Independent Ta Centers Supported on Two-Dimensional TiO2 Nanosheets

Highly-dispersed, supported oxides are ubiquitous solid catalysts, but they can be challenging to characterize with atomic precision. Here it is shown that crystalline anatase TiO2 nanosheets (~5 nm thick) are ideal supports for imaging highly-dispersed active sites. Ta cations are deposited by several routes, and high-resolution high angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) is used to determine the location of Ta with respect to the TiO2 lattice and to quantify Ta-Ta distances. In the best case, it is shown that >80% of Ta atoms are isolated from one another, whereas other techniques are blind to this critical catalytic property or give only qualitative estimates. TiO2 nanosheets may prove to be a useful platform for other types of catalysis studies