Linking Grain Boundaries and Grain Growth in Ceramics

The macroscopic properties of most materials are strongly influenced by grain size. In ceramic materials the microstructure usually results from the sintering process. Understanding the basic mechanisms of grain growth on an atomic length scale in ceramics would be beneficial to tailor the microstructure for improved macroscopic performance of devices. A method is presented using grain growth experiments to select samples for closer examination of grain boundaries with transmission electron microscopy. The growth experiments are used to identify temperatures were changes at grain boundaries occur at high temperature. Subsequently samples of interest are investigated using transmission electron microscopy (TEM) methods. The correlation between TEM results and changes in grain growth behavior can be used to gain closer insight into the processes occurring during grain growth at an atomic length scale. Strontium titanate is used as model system to demonstrate the combination of growth experiments with TEM results. Normal grain growth shows two distinct drops in growth rate in the temperature range between 1 300 and 1 425 °C, independent of the A‐site to B‐site stoichiometry of the perovskite. In previous studies a high preference for grain boundary planes oriented parallel to the 100 direction of one of the adjacent grains was found in the high temperature regime. This study shows that the preference does not exist in the low temperature regime possibly explaining the change in grain growth rate.     

Latent risk and trend models for the evolution of annual fatality numbers in 30 European countries

In this paper a unified methodology is presented for the modelling of the evolution of road safety in 30 European countries. For each country, annual data of the best available exposure indicator and of the number of fatalities were simultaneously analysed with the bivariate latent risk time series model. This model is based on the assumption that the amount of exposure and the number of fatalities are intrinsically related. It captures the dynamic evolution in the fatalities as the product of the dynamic evolution in two latent trends: the trend in the fatality risk and the trend in the exposure to that risk. Before applying the latent risk model to the different countries it was first investigated and tested whether the exposure indicator at hand and the fatalities in each country were in fact related at all. If they were, the latent risk model was applied to that country; if not, a univariate local linear trend model was applied to the fatalities series only, unless the latent risk time series model was found to yield better forecasts than the univariate local linear trend model. In either case, the temporal structure of the unobserved components of the optimal model was established, and structural breaks in the trends related to external events were identified and captured by adding intervention variables to the appropriate components of the model. As a final step, for each country the optimally modelled developments were projected into the future, thus yielding forecasts for the number of fatalities up to and including 2020.     

Huge increase of therapeutic window at a bioactive silver/titania nanocomposite coating surface compared to solution

A silver containing coating used in the human body, e.g., on an implant should be both effectively antimicrobial and non-cytotoxic to human cells. It is generally believed that the biologic effect originates from silver ions released from the coating. Nanocomposites with well controlled Ag filling factor were prepared by co-sputtering, and the silver surface concentration and the silver release were determined by XPS and ICP-MS, respectively. Here we show that only a small therapeutic window exists for dissolved silver but the therapeutic window is largely increased at the surface. While the toxicity observed for mammalian cells in contact with the bioactive Ag/TiO₂ nanocomposite surface and for silver ions in solution is rather similar the antimicrobial activity is drastically enhanced at the surface. A model is proposed to explain the strong increase of the antimicrobial activity at the surface. The present results not only question well-established tests for antimicrobial activity but they are also important for the design of antimicrobial coatings, e.g., for biomedical devices.     

A First‐Principles Investigation of the Compositional Dependent Properties of Magnetic Shape Memory Heusler Alloys

The interplay of structural and magnetic properties of magnetic shape memory alloys is closely related to their composition. In this study the influence of the valence electron concentration on the tetragonal transformation in Ni₂Mn_{1 + x}Z_{1 ? x} (Z = Ga, In, Sn, Sb) and Co₂Ni_{1 + x}Ga_{1 ? x} is investigated by means of ab initio calculations. While the type of magnetic interaction is different for the two series, the trends of the total energy changes under a tetragonal transformation are very similar. We find that tetragonal structures become energetically preferred with respect to the cubic one as the valence electron concentration e/a is increased regardless of the system under consideration. In particular, the energy difference between the austenite and martensite structures increases linearly with e/a, which is in part responsible for the linear increase of the matensite transformation temperature. The substitution of nickel by platinum increases even further the transformation temperature.