Modal Kleene Algebra and Partial Correctness

Modal Kleene algebras are relatives of dynamic logics that support program construction and verification by equational reasoning. We describe their application in implementing versatile program correctness components in interactive theorem provers such as Isabelle/HOL. Starting from a weakest precondition based component with a simple relational store model, we show how variants for Hoare logic, strongest postconditions and program refinement can be built in a principled way. Modularity of the approach is demonstrated by variants that capture program termination and recursion, memory models for programs with pointers, and program trace semantics.Engineering and Physical Sciences Research Council (Grant ID: REMS: Rigorous Engineering for Mainstream Systems, EP/K008528/1)This is the author accepted manuscript. It is currently under an indefinite embargo pending publication by Springer

Future climate impact on spruce bark beetle life cycle in relation to uncertainties in regional climate model data ensembles

In this study, we quantify the effect of uncertainties in climate projections on an impact model (IPS) that describes the temperature-dependent swarming and development of Ips typographus. Three forcing climate data sets (ensembles) were used: (1) E-Obs gridded observations, (2) ERA-40 reanalysis data downscaled by eight regional climate models (RCMs) and (3) regional scenarios from one RCM forced by seven GCM simulations representing SRES-A1B, for the period of 1961-2097. The IPS_RCM_ERA40 ensemble members, including IPS_RC3_ERA40, were generally within the IPS_E-Obs confidence limits. The IPS model is however sensitive to the warming during spring and cooling during autumn, and deviations in simulated swarming were related to known climate model biases. The variation between the IPS_RCA3_GCM ensemble members was particularly high in regions where warmer summers (temperature increase from +2 degrees C to +4 degrees C) will induce an additional generation per year, for example a shift from one to two generations per year in south Scandinavia, and an increased frequency of three generations per year in central Europe. Impact assessments based on an ensemble of climate data gives more robust decision support than a single climate model approach because it allows a probabilistic assessment of the geographical areas experiencing a transition in biological response

Controlling the catalytic bond breaking selectivity of Ni surfaces by step blocking

The reactivity of catalytic surfaces is often dominated by very reactive low-coordinated atoms such as step-edge sites1-11. However, very little knowledge exists concerning the influence of step edges on the selectivity in reactions involving multiple reaction pathways. Such detailed information could be very valuable in rational design of new catalysts with improved selectivity. Here we show, from an interplay between scanning tunnelling microscopy experiments and density functional theory calculations, that the activation of ethylene on Ni(111) follows the trend of higher reactivity for decomposition at step edges as compared with the higher-coordinated terrace sites. The step-edge effect is considerably more pronounced for the C-C bond breaking than for the C-H bond breaking, and thus steps play an important role in the bond-breaking selectivity. Furthermore, we demonstrate how the number of reactive step sites can be controlled by blocking the steps with Ag. This approach to nanoscale design of catalysts is exploited in the synthesis of a new high-surface-area AgNi alloy catalyst, which is tested in hydrogenolysis experiments