Publications

A review is presented of the history of the development of the Point Defect Model (PDM) for the growth and breakdown of passive films that form on the surfaces of reactive metals in contact with corrosive, condensed phase environments. The PDM has passed through three generations, with each successive generation addressing issues that have arisen from experiment. Thus, the first Generation model (PDM-I), which was developed in the late 1970s/early 1980s, assumed that the passive film was a single defective oxide layer that contained cation vacancies and oxygen vacancies that were generated and annihilated at the metal/film and film/solution interfaces. This model was inspired by the work by Wagner on high temperature oxidation. As with gas-phase systems, the film was assumed not to dissolve. However, it soon became evident that this model could not account for the properties of the passive state on metals in contact with aqueous environments and, accordingly a Generation II model (PDM-II) was developed to address these issues. PDM-II incorporated the bi-layer structure of the film comprising a defective oxide (or hydride) barrier layer that grows into the metal and an outer layer that forms by precipitation of material from the reaction of cations transmitted through the barrier layer with species in the environment (including water, CO 3 2− , HS−, etc.), introduced metal interstitials to the suite of defects, recognized barrier layer dissolution, and recognized the need to classify reactions as to whether they are lattice conservative or non-conservative. PDM-II has enjoyed considerable success and the author knows of no instance where it has been demonstrated to be at odds with experiment when confluence between experiment and theory has been demonstrated. A Generation III model (PDM-III) has been recently developed to extend the theory to those cases (e.g., the valve metals) where the outer layer is so resistive that it controls the impedance of the interface and hence the corrosion rate. A fourth generation model that will describe passivity on alloys is now under development. The experimental evidence upon which each generation is based is reviewed.

Abstract The effects of interaction with surrounding water on the dynamic response behaviour of cantilever tower structures are studied. Expressions for response to harmonic ground motion in individual modes of vibration, including hydrodynamic interaction, are presented, the accuracy of responses obtained by ignoring surface waves and compressibility of water in the hydrodynamic solutions is evaluated, the effects of hydrodynamic interaction on the fundamental period of vibration are studied and the commonly used ‘added mass’ approach to account for effects of surrounding water is examined. The conclusions deduced from the results of this investigation include the following. Interaction with surrounding water increases the fundamental period of vibration of the tower and decreases the modal damping ratio. Compressibility of water has essentially no influence in the hydrodynamic effects on slender towers. The traditional definition of added mass is conceptually deficient, but is simple to employ; the errors in this simple added mass representation are negligible for the first mode of vibration of towers.

We sampled isolated trees and tree clusters from a blue oak, Quercus douglasii, savanna to determine the spatial heterogeneity of fine root biomass and soil carbon across the landscape as a function of tree size and configuration. We aimed to understand how fine root structure enables sustained ecosystem metabolism through a summer of limited moisture and high heat and facilitates resource acquisition during the short period of high resource supply. An additional goal was to provide a basis for upscaling root biomass and soil carbon to the landscape scale. We sampled trees of different size and tree clusters via a stratified sampling scheme that accounted for spatial heterogeneity in root biomass and soil carbon with lateral distance from the tree bole, or cluster centre, and soil depth. We upscaled these estimates using site-specific information from a lidar survey. We found that fine roots and soil carbon are spatially heterogeneous in their landscape distribution and greatly increase with tree size. We also found that Q.douglasii possesses a dimorphic fine root architecture, uniquely suited to the region's climatic constraints and exhibits morphological plasticity among trees of different size and physical setting.

We present a computational framework for stereopsis based on the outputs of linear spatial filters tuned to a range of orientations and scales. This approach goes beyond edge-based and area-based approaches by using a richer image description and incorporating several stereo cues that previously have been neglected in the computer vision literature. A technique based on using the pseudo-inverse is presented for characterizing the information present in a vector of filter responses. We show how in our framework viewing geometry can be recovered to determine the locations of epipolar lines. An assumption that visible surfaces in the scene are piecewise smooth leads to differential treatment of image regions corresponding to binocularly visible surfaces, surface boundaries, and occluded regions that are only monocularly visible. The constraints imposed by viewing geometry and piecewise smoothness are incorporated into an iterative algorithm that gives good results on random-dot stereograms, artificially generated scenes, and natural grey-level images.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Abstract Unter Verwendung von Phasen‐Transfer‐Katalysatoren wie Tetrabutyl‐ammoniumchlorid oder Adogen 464 werden nucleophile Substitutionsreaktionen an polymeren funktionellen Verbindungen diskutiert.