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Gummow R.J.,James Cook UniversityTownsville | Sharma N.,University of South Australia | Feng R.,James Cook UniversityTownsville | Feng R.,Pennsylvania State UniversityUniversity Park | And 3 more authors.
Journal of the Electrochemical Society | Year: 2013

Li1.0(Li1/7Mn4/7 Ni2/7]O2 cathode material was prepared by a facile, one-pot synthesis method. The structure of the material was determined by Rietveld refinement of structural models using high-resolution synchrotron X-ray and neutron powder diffraction data and was found to consist of two distinct phases. The major phase, with composition Li1.25(3)Ni0.17(1) Mn0.61(1)O2, close to the well-characterized Li1.2Ni0.2Mn0.6O2 composition can be described as an intergrowth structure of Li2MnO3.i and LiMn0.5Ni0.5O2 domains and the second phase is a lithium-deficient layered structure with refined composition Li0.85(1)Ni0.57(1)Mn0.55(1)O2. The composite cathode has a high initial discharge capacity of 250 mAh/g which drops to 225 mAh/g on the 2nd discharge cycle. This capacity is maintained on .subsequent cycles. Time-resolved in-situ synchrotron XRD data was used to study the changes in the lattice parameters and phase evolution of the two phases during Li-insertion and extraction. © 2013 The Electrochemical Society. All rights reserved.

Lough J.M.,James Cook UniversityTownsville | Cantin N.E.,A Healthy and Resilient Great Barrier Reef Research ProgramAustralian Institute of Marine Science | Benthuysen J.A.,Sustainable Coastal Ecosystems and Industries in Tropical Australia Research ProgramAustralian Institute of Marine Science | Cooper T.F.,A Healthy and Resilient Great Barrier Reef Research ProgramAustralian Institute of Marine Science
Limnology and Oceanography | Year: 2015

Sustained calcification is fundamental for maintaining tropical coral reef ecosystems which are under increasing pressure from global and local changes to the marine environment. Annual density bands in massive corals provide a robust means to retrospectively monitor growth and identify the environmental drivers. We present Porites growth characteristics for 60 coral cores from 18 reef sites and five environmental regions off Western Australia (WA) over the period 1950-2008. This remote region encompasses diverse coral reef ecosystems and is an economically important natural resource hub. Despite high variability, average calcification is highest in the offshore shelf reefs and lowest in the most southerly reefs. The primary environmental drivers of these spatial variations are annual and winter minimum sea surface temperature (SST) and annual winter minimum photosynthetically active radiation. Average growth characteristics for WA reefs are comparable to those of Australia's Great Barrier Reef. Calcification rates at the two most southerly WA reefs are anomalously high, which may be due to the unusual environmental conditions generated by the Leeuwin Current. Variable rates of SST warming across the 18 reefs are, however, changing the strength of the relationship between SST and calcification. We found no evidence to support the contention that annual density banding is driven by environmental seasonality. Retrospective monitoring of growth rates provides a critical tool for both assessing coral growth responses to ongoing rapid climate change and possible responses to increasing anthropogenic pressures related to natural resource development in the region. © 2015 Association for the Sciences of Limnology and Oceanography.

Mao Y.,Hubei University | Ridd P.V.,James Cook UniversityTownsville
Journal of Geophysical Research C: Oceans | Year: 2015

Accurate parameterization of spatially variable diffusivity in complex shelf regions such as the Great Barrier Reef (GBR) lagoon is an unresolved issue for hydrodynamic models. This leads to large uncertainties to the flushing time derived from them and to the evaluation of ecosystem resilience to terrestrially derived pollution. In fact, numerical hydrodynamic models and analytical cross-shore diffusion models have predicted very different flushing times for the GBR lagoon. Nevertheless, scarcity of in situ measurements used previously in the latter method prevents derivation of detailed diffusivity profiles. Here detailed cross-shore profiles of diffusivity were calculated explicitly in a closed form for the first time from the steady state transects of sea surface temperature for different sections of the GBR lagoon. We find that diffusivity remains relatively constant within the inner lagoon (<∼20 km) where tidal current is weak, and increases linearly with sufficiently large tidal amplitude in reef-devoid regions, but increases dramatically where the reef matrixes start and fluctuates with reef size and density. The cross-shelf profile of steady state salinity calculated using the derived diffusivity values agrees well with field measurements. The calculated diffusivity values are also consistent with values derived from satellite-tracked drifters. Flushing time by offshore diffusion is of the order of 1 month, suggesting the important role of turbulent diffusion in flushing the lagoon, especially in reef-distributed regions. The results imply that previous very large residence times predicted by numerical hydrodynamic models may result from underestimation of diffusivity. Our findings can guide parameterization of diffusivity in hydrodynamic modeling. © 2015. American Geophysical Union.

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