Geometrically necessary dislocation densities in olivine obtained using high-angular resolution electron backscatter diffraction

© 2016 The AuthorsDislocations in geological minerals are fundamental to the creep processes that control large-scale geodynamic phenomena. However, techniques to quantify their densities, distributions, and types over critical subgrain to polycrystal length scales are limited. The recent advent of high-angular resolution electron backscatter diffraction (HR-EBSD), based on diffraction pattern cross-correlation, offers a powerful new approach that has been utilised to analyse dislocation densities in the materials sciences. In particular, HR-EBSD yields significantly better angular resolution (<0.01°) than conventional EBSD (~0.5°), allowing very low dislocation densities to be analysed. We develop the application of HR-EBSD to olivine, the dominant mineral in Earths upper mantle by testing (1) different inversion methods for estimating geometrically necessary dislocation (GND) densities, (2) the sensitivity of the method under a range of data acquisition settings, and (3) the ability of the technique to resolve a variety of olivine dislocation structures. The relatively low crystal symmetry (orthorhombic) and few slip systems in olivine result in well constrained GND density estimates. The GND density noise floor is inversely proportional to map step size, such that datasets can be optimised for analysing either short wavelength, high density structures (e.g. subgrain boundaries) or long wavelength, low amplitude orientation gradients. Comparison to conventional images of decorated dislocations demonstrates that HR-EBSD can characterise the dislocation distribution and reveal additional structure not captured by the decoration technique. HR-EBSD therefore provides a highly effective method for analysing dislocations in olivine and determining their role in accommodating macroscopic deformation

Marnda Gardairri: Facilitation of an Indigenous Ranger Rock Art Workshop

The Marnda Gardairri Indigenous Rangers Workshop was held from 3–5 October 2017 on the Burrup Peninsula in the Pilbara region of Western Australia. The event, which was hosted by the Murujuga Aboriginal Corporation (MAC), brought together rangers from across Australia to discuss rock art conservation and management. The workshop was given the title ‘Marnda Gardairri’ as this means rock scratching/engraving on the Burrup Peninsula. The workshop was developed by MAC in collaborative partnership with Rio Tinto Iron Ore-Pilbara Operations and the Nulungu Research Institute (The University of Notre Dame Australia). Rio Tinto and Woodside Petroleum funded the workshop, with Mel Marshall and Lynley Wallis of Nulungu engaged to coordinate and facilitate the event, assisted by Kate Golson.https://researchonline.nd.edu.au/nulungu_insights/1002/thumbnail.jp

Engineering novel complement activity into a pulmonary surfactant protein

Complement neutralizes invading pathogens, stimulates inflammatory and adaptive immune responses, and targets non- or altered-self structures for clearance. In the classical and lectin activation pathways, it is initiated when complexes composed of separate recognition and activation subcomponents bind to a pathogen surface. Despite its apparent complexity, recognition-mediated activation has evolved independently in three separate protein families, C1q, mannose-binding lectins (MBLs), and serum ficolins. Although unrelated, all have bouquet-like architectures and associate with complement-specific serine proteases: MBLs and ficolins with MBL-associated serine protease-2 (MASP-2) and C1q with C1r and C1s. To examine the structural requirements for complement activation, we have created a number of novel recombinant rat MBLs in which the position and orientation of the MASP-binding sites have been changed. We have also engineered MASP binding into a pulmonary surfactant protein (SP-A), which has the same domain structure and architecture as MBL but lacks any intrinsic complement activity. The data reveal that complement activity is remarkably tolerant to changes in the size and orientation of the collagenous stalks of MBL, implying considerable rotational and conformational flexibility in unbound MBL. Furthermore, novel complement activity is introduced concurrently with MASP binding in SP-A but is uncontrolled and occurs even in the absence of a carbohydrate target. Thus, the active rather than the zymogen state is default in lectin·MASP complexes and must be inhibited through additional regions in circulating MBLs until triggered by pathogen recognition

Alaska-Canada Rail Link Economic Benefits

Construction of the 1,740 km Alaska-Canada Rail Link (ACRL) between Fort Nelson, BC and Delta Junction, Alaska to join the North American rail system to the Alaska Railroad will result in tremendous economic benefits for Canada and the US. The ACRL will provide valuable additional east-west rail capacity and tidewater access to the Pacific, hugely benefitting not only the Yukon and Eastern Alaska regions, into which it will introduce rail transport for the first time, but throughout both countries. The economic benefits of ACRL construction are consistent with Canadian government’s desire to promote Northern development and comparable in significance to those of Canadian Pacific Railway in the 1880’s and the St. Lawrence Seaway in the 1950’s. Construction of the ACRL alone will bring unprecedented economic stimulus to the region in terms of job creation, wages and income tax revenue over multiple years. Table 7-1 below summarizes the benefits from ACRL construction for the Yukon, BC and Canada as a whole. However, these estimates are conservative as they exclude benefits associated with pre-construction activities, railway operation post-construction, sales taxes and corporate taxes as well as all such benefits that will accrue to Alaska and the US

A new map-making algorithm for CMB polarisation experiments

With the temperature power spectrum of the cosmic microwave background (CMB) at least four orders of magnitude larger than the B-mode polarisation power spectrum, any instrumental imperfections that couple temperature to polarisation must be carefully controlled and/or removed. Here we present two new map-making algorithms that can create polarisation maps that are clean of temperature-to-polarisation leakage systematics due to differential gain and pointing between a detector pair. Where a half wave plate is used, we show that the spin-2 systematic due to differential ellipticity can also by removed using our algorithms. The algorithms require no prior knowledge of the imperfections or temperature sky to remove the temperature leakage. Instead, they calculate the systematic and polarisation maps in one step directly from the time ordered data (TOD). The first algorithm is designed to work with scan strategies that have a good range of crossing angles for each map pixel and the second for scan strategies that have a limited range of crossing angles. The first algorithm can also be used to identify if systematic errors that have a particular spin are present in a TOD. We demonstrate the use of both algorithms and the ability to identify systematics with simulations of TOD with realistic scan strategies and instrumental noise.Comment: 11 pages, 6 figure

Accounting for multivariate probabilities of failure in vertical seawall reliability assessments

The aim of this paper is to appraise the current knowledge on seawall performance and reliability, and to make the case for improved reliability assessments of vertical seawalls, which are used here as a representative for coastal flood defences. In order to achieve this aim, a brief introduction to flood risk management is first given. Then, vertical seawalls are introduced, and their most prominent failure modes are discussed. Reliability analysis is introduced within the context of flood risk management. More specifically, the fragility curve approach that is currently in use in industry is described, and its limitations are discussed. Finally, it is argued that recent advances in multivariate extreme value models would enable improvements to the approaches currently applied in practice. It is stressed that future risk assessment models of coastal flood defences ought to include multiple failure modes and their interactions, a thorough analysis of the model uncertainties, and potential computational costs, in view of providing practitioners with an improved and functional risk assessment tool. Carter, Magar, Simm, Gouldby & Walli