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Understanding how enzyme catalysis varies with temperature is key to understanding catalysis itself, and ultimately, how to tune temperature optima. Temperature dependence studies inform on the change in heat capacity during the reaction, Δ ‡ , and we have recently demonstrated that this can expose links between the protein free energy landscape and enzyme turnover. By quantifying Δ ‡ , we capture information on the changes to the distribution of vibrational frequencies during enzyme turnover. The primary experimental tool to probe the role of vibrational modes in a chemical/biological process is isotope effect measurements, since isotopic substitution primarily affects the frequency of vibrational modes at/local to the position of isotopic substitution. We have monitored the temperature dependence of a range of isotope effects on the turnover of a hyper-thermophilic glucose dehydrogenase. We find a progressive effect on the magnitude of Δ ‡ with increasing isotopic substitution of D-glucose. Our experimental findings, combined with molecular dynamics simulations and quantum mechanical calculations, demonstrate that Δ ‡ is sensitive to isotopic substitution. The magnitude of the change in Δ ‡ due to substrate isotopic substitution indicates that small changes in substrate vibrational modes are 'translated' into relatively large changes in the (distribution and/or magnitude of) enzyme vibrational modes along the reaction. Therefore, the data suggest that relatively small substrate isotopic changes are causing a significant change in the temperature dependence of enzymatic rates.

In this work, we present a model of fission gas behavior in U 3 Si 2 under light water reactor (LWR) conditions for application in engineering fuel performance codes. The model includes components for intra-granular and inter-granular behavior of fission gases. The intra-granular component is based on cluster dynamics and computes the evolution of intra-granular fission gas bubbles and swelling coupled to gas diffusion to grain boundaries. The inter-granular component describes the evolution of grain-boundary fission gas bubbles coupled to fission gas release. Given the lack of experimental data for U 3 Si 2 under LWR conditions, the model is informed with parameters calculated via atomistic simulations. In particular, we derive fission gas diffusivities through density functional theory calculations, and the re-solution rate of fission gas atoms from intra-granular bubbles through binary collision approximation calculations. The developed model is applied to the simulation of an experiment for U 3 Si 2 irradiated under LWR conditions available from the literature. Results point out a credible representation of fission gas swelling and release in U 3 Si 2 . Finally, we perform a sensitivity analysis for the various model parameters. Based on the sensitivity analysis, indications are derived that can help in addressing future research on the characterization of the physical parameters relative to fission gas behavior in U 3 Si 2 . The developed model is intended to provide a suitable infrastructure for the engineering scale calculation of fission gas behavior in U 3 Si 2 that exploits a multiscale approach to fill the experimental data gap and can be progressively improved as new lower-length scale calculations and validation data become available.

A novel metal supported Solid Oxide Fuel Cell has been developed, capable of operating at temperatures of 500-600°C. The rationale behind the materials used to construct this fuel cell type is given, and results presented from cell and short stack testing, including durability and thermal cycling trials. This new fuel cell variant is shown to be tolerant of carbon monoxide durable, robust to thermal and redox cycling, and capable of delivering technologically relevant power densities.

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