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

Introduction to algorithms for managing the common trauma patient

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An Inquiry: Effectiveness of the Complex Empirical Mode Decomposition Method, the Hilbert-Huang Transform, and the Fast-Fourier Transform for Analysis of Dynamic Objects

A review of current signal analysis tools show that new techniques are required for an enhanced fidelity or data integrity. Recently, the Hilbert-Huang transform (HHT) and its inherent property, the Empirical Mode Decomposition (EMD) technique, have been formerly investigated. The technique of Complex EMD (CEMD) was also explored. The scope of this work was to assess the CEMD technique as an innovative analysis tool. Subsequent to this, comparisons between applications of the Hilbert transform (HT) and the Fast-Fourier transform (FFT) were analyzed. MATLAB was implemented to model signal decomposition and the execution of mathematical transforms for generating results. The CEMD technique successfully decomposed the data into its oscillatory modes. After comparative graphical analysis of the HT and FFT, application of the HT provided marginal enhancements of the data modeled previously by the FFT. Altogether, the HHT could not be determined as a helpful analysis tool. Nevertheless, the CEMD technique, an inherent component of the HHT, exhibited a possible improvement as an analysis tool for signal processing data. Further evaluation of the CEMD technique and the HHT is needed for ultimate determination of their usefulness as an analysis tool

Influences on conifer drought responses in northern California

California is experiencing increasingly severe and prolonged droughts, which are contributing to changes in tree stress and forest mortality. Many factors affect a tree’s drought response, including competition, climate, and site and tree characteristics. Northern California provides a suitable venue to explore the effects of these factors, as it spans a variety of site conditions and includes habitat for conifers with different adaptations and requirements. This study used annual 13C discrimination and growth metrics to assess differences in drought resistance and resilience in conifers adapted to coastal and montane ranges at both wet and dry sites, as well as differences in environmental factors that affect species-level drought responses. Coastal species (Sitka spruce and western hemlock) were more sensitive to drought than montane species (Shasta fir, Brewer spruce, sugar pine, and western white pine). Coastal trees were more sensitive to drought at dry sites than wet sites. Montane species exhibited smaller differences in drought resistance between wet and dry conditions, but varied in factors contributing to physiological response among species. This study suggests that in most situations, conifers in northern California weathered the 2012 – 2016 drought with reasonably high resistance and resilience. However, many of these trees may be at risk for increased stress and mortality in the event of longer and/or more frequent, severe drought. Management strategies for conifers in one region may not be suitable for the same species in another region, and the effects of competition and community composition on drought resistance and resilience must be carefully considered