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J Thomas Sanderson, Associate Professor, Institut National de la Recherche Scientifique-Institute Armand-Frappier, Université du Québec, Montréal, QC, H9R IG6, Canada tells of the importance of the aromatase enzyme, pesticide interactions with the enzyme and the possibility of endocrine disruption effects. © 2006. Research Information Ltd. All rights reserved.

Results of hydrogen diffusion in copper are obtained based on molecular dynamics simulations. Temperature dependent diffusion coefficient values obtained here from the simulations agree well with experimental reports in the literature over a wide range spanning 300 K to 1330 K. Simulations with and without a grain boundary have also been carried out to probe their role on hydrogen outgassing from copper, a typical material for electrodes in high pulsed power systems. The results obtained show increased out-diffusion in the presence of a grain boundary (GB), and anisotropic transport, with increases parallel to the GB plane and reduction in the normal direction. The behavior likely arises from distortion of atoms in the GB region which provide alternate paths for atomic hops within the GB core. This result suggests that capping the metal surface, by a few nanolayers of a suitable coating or an oxide, may help reduce outgassing from the grain boundaries inherent in the copper material. In this research, a thin tungsten layer (a few monolayers thick) was added to arrest the outgassing from the metallic copper. It was observed that with inclusion of the tungsten layer, the diffusion rate became very negligible compared to the situation without the tungsten layer.

Modern simulation software commonly requires the solution to physical elements such as the electric eld over complex geometries. The solution is computed by numerical methods which solve for Poisson's equation over a domain space. Iterative methods, such as the Jacobi method, are computationally expensive without assumptions about the domain which reduce the complexity. While an increase in computational power by means of parallelization generally improves the runtime, the implementation of numerical techniques such as the multigrid method demonstrate large runtime improvements without a reduction in solution accuracy. The development of a numerical solver for Poisson's equation utilizing the multigrid method and implemented for GPU parallel processing is detailed. The solver is tested against analytical solutions and a Red-Black Jacobi numerical solver used in a previously developed Particle-in-Cell Monte Carlo collision simulation software. The results demonstrate that the multigrid based GPU solver produced a solution of equal accuracy in less time for all cases.

Molecular dynamics (MD) simulations were carried out to study the potential for material degradation from a copper nanoprotrusion under high electric field conditions. The distribution of Maxwell tensile stress and Joule heating induced by electric field of a three-dimensional system were calculated based on COMSOL software. Those results were used in LAMMPS to simulate the operations of nanoprotrusion in various settings. The simulations consist of two different methods. The first method employed constant temperature for each run. Several simulations for same model were performed by running at different temperatures to probe the effect of Joule heating of the nanoprotrusion. A second method was then also advanced which allowed for heating within each MD simulation. The system was then subjected to increasing temperatures when an external electric field was applied. The results in this thesis show that mass ejection from a nanoprotrusion will take place when the electric field surrounding the nanoprotrusion is strong enough. The model with higher field was also influenced by a stronger Maxwell stress and higher temperatures. Both of these factors drive the structural instability. In the case with a 3 V/nm field applied, the mass ejection through the tip was predicted when the nanoprotrusion was heated up by the high current density. Besides, it was shown that the electric field gets enhanced when the shape of nanoprotrusion has a higher aspect ratios. In this scenario, the requirement of field and temperature for mass ejection is predicted to reduce.