Early afterdepolarisations and ventricular arrhythmias in cardiac tissue: a computational study

Afterdepolarisations are associated with arrhythmias in the heart, but are difficult to study experimentally. In this study we used a simplified computational model of 1D and 2D cardiac ventricular tissue, where we could control the size of the region generating afterdepolarisations, as well as the properties of the afterdepolarisation waveform. Provided the size of the afterdepolarisation region was greater than around 1 mm, propagating extrasystoles were produced in both 1D and 2D. The number of extrasystoles produced depended on the amplitude, period, and duration of the oscillatory EAD waveform. In 2D, re-entry was also initiated for specific combinations of EAD amplitude, period, and duration, with the afterdepolarisation region acting as a common pathway. The main finding from this modelling study is therefore that afterdepolarisations can act as potent sources of propagating extrasystoles, as well as a source of re-entrant activation

Scenario-based serious games repurposing

Serious games are very content-rich forms of educational media, often combining high fidelity visual and audio content with diverse pedagogic approaches. This paper introduces scenario-based serious games repurposing and demonstrates repurposing a serious game into new learning objects. The process uses the scenario editor called "mEditor". Two case studies based on the Happy Night Club serious game are presented. The article describes exploratory work which continues the work that started within the mEducator project regarding repurposing serious games in order to enable their use and reuse in the same or different educational contexts

E-commerce transactions in a virtual environment: Virtual transactions

E-commerce is a fundamental method of doing business, such that for a firm to say it is trading at all in the modern market-place it must have some element of on-line presence. Coupled with this is the explosion of the "population" of Massively Multiplayer On-line Role Playing Games and other shared virtual environments. Many suggest this will lead to a further dimension of commerce: virtual commerce. We discuss here the issues, current roadblocks and present state of an e-commerce transaction carried out completely within a virtual environment; a virtual transaction. Although technically such transactions are in a sense trivial, they raise many other issues in complex ways thus making V-transactions a highly interesting cross-disciplinary issue. We also discuss the social, ethical and regulatory implications for the virtual communities in these environments of such v-transactions, how their implementation affects the nature and management of a virtual environment, and how they represent a fundamental merging of the real and virtual worlds for the purpose of commerce. We highlight the minimal set of features a v-transaction capable virtual environment requires and suggest a model of how in the medium term they could be carried out via a methodology we call click-through, and that the developers of such environments will need to take on the multi-modal behavior of their users, as well as elements of the economic and political sciences in order to fully realize the commercial potential of the v-transaction. © 2012 Springer Science+Business Media, LLC

Simulation of the delamination of thin films

We simulate thin film delamination using a lattice springs model. We use this model to construct a phase diagram of different delamination behaviours, produced by varying the compression of the film and also the radius to which local relaxation is allowed to take place about failing bonds. From this we see a progression from laminar and linear behaviours to radial and rounded features as compressive stress is increased. Sinusoidal telephone cord behaviour occurs only at a small range of fairly low stresses, and thin films. © EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2005

Kinetic Monte Carlo and density functional study of hydrogen enhanced dislocation glide in silicon

We investigate Hydrogen Enhanced Dislocation Glide [HEDG], using n-fold way Kinetic Monte Carlo simulations of the interaction between hydrogen and 90° partial dislocations in silicon, and a range of new density functional calculations. We examine two different hydrogen arrival species, as well as hydrogen recombination at the dislocation. The Monte Carlo simulations use a line-wise description of the dislocation line parameterized using density functional calculations of migration and formation energies of various dislocation line defects and their complexes with hydrogen. From this we suggest that the rate of H2 expulsion from the dislocation core increases as we approach HEDG, but that if the concentration of the hydrogen species goes beyond that required for HEDG it then slows dislocation motion by choking the line with defects comprised of two hydrogen atoms in a reconstruction bond. A `dislocation engine' model is proposed whereby hydrogen enters the dislocation line, catalyses motion, and is expelled along the core as H2

Kinetic Monte Carlo study of dislocation motion in silicon: Soliton model and hydrogen enhanced glide

The problems with dislocations in semiconductors are becoming tractable with modern computing by hybrid techniques. These apply static first principles calculations of energetics for important processes (e.g. kink formation and migration energies) and kinetic Monte Carlo techniques to follow the dynamic interaction of these processes over length and time scales inaccessible to, for example, molecular dynamic simulation. The simplest model system for covalent and ceramic solids is silicon, but there is debate over the structure and properties of dislocations there. The movement of the dislocation by the simple bond switching mechanism was studied from first principles, finding activation energies close to experiment, but lately the alternative mechanism invoking free radicals or solitons was found to give similar energies. We report results from an n-fold way kinetic Monte Carlo approach, applied to a simple system to verify the standard model for kink pair nucleation limited dislocation glide (the Hirth-Lothe model). We then apply an improved technique to the kinetics of the soliton model and to hydrogen enhanced dislocation glide. © 2001 Elsevier Science B.V. All rights reserved

Linewise kinetic Monte Carlo study of silicon dislocation dynamics

We present a number of n-fold way kinetic Monte Carlo simulations of the glide motion of 90° partial dislocations in silicon. We undertake a survey of ratios of kink formation energy Fk to kink migration barrier Wm, over a range of temperatures and applied stresses. These simulations are compared with Hirth-Lothe theory and an extension to the Hirth-Lothe theory of Kawata and Ishiota. The latter is found to give the best description of the system. Using literature first principle values for the kink and soliton formation and migration energies, a model combining both strained bond and soliton mediated motion shows a negligible contribution to dislocation motion from the solitons. The high soliton pair creation barrier was limiting and a soliton mediated mechanism for dislocation motion would have to achieve thermal equilibrium concentration via impurity or point defect interaction to be effective. We also show that if this can be overcome solitons greatly increase the mobility of the dislocation, even without a binding energy between solitons and kinks. The simulation coded here is easily expandable to incorporate further dislocation line effects such as impurities at the line

Kinetic Monte Carlo study of dislocation motion in silicon: Soliton model and hydrogen enhanced glide

The problems with dislocations in semiconductors are becoming tractable with modern computing by hybrid techniques. These apply static first principles calculations of energetics for important processes (e.g. kink formation and migration energies) and kinetic Monte Carlo techniques to follow the dynamic interaction of these processes over length and time scales inaccessible to, for example, molecular dynamic simulation. The simplest model system for covalent and ceramic solids is silicon, but there is debate over the structure and properties of dislocations there. The movement of the dislocation by the simple bond switching mechanism was studied from first principles, finding activation energies close to experiment, but lately the alternative mechanism invoking free radicals or solitons was found to give similar energies. We report results from an n-fold way kinetic Monte Carlo approach, applied to a simple system to verify the standard model for kink pair nucleation limited dislocation glide (the Hirth-Lothe model). We then apply an improved technique to the kinetics of the soliton model and to hydrogen enhanced dislocation glide. © 2001 Elsevier Science B.V. All rights reserved