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Studies of high dpa ion beam irradiation effects on fcc AA-6061 and fcc-bcc duplex steel 2205: micromechanical modelling and nano-indentation examination of hardness variations.
No full textThe irradiation effects of high dpa and the ramification on the engineering assessment of reactor components in GEN IV systems is of considerable interest. Most polycrystalline metallic materials derive their strengths from the interactions of dislocations with defects such as solid solution alloying elements, interstitial elements, other dislocations, grain boundaries and sub-microscopic precipitates. Irradiation of metals and alloys at temperatures below those that anneal their defects typically produces pronounced radiation hardening, this is investigated herein to better understand the application of complex alloys in future reactor systems. .
The current study focuses on ion beam irradiation of AA6061 and Duplex steel 2205, utilising the ANATRES Accelerator at ANSTO with 12 MeV Au+5 ions used as the irradiating ions. To induce a 100 dpa damage, often cited as the operating level of GEN IV reactor, heavy Au+5 ions are necessary as self-ion irradiation would fail to induce the required damage. The main attribute of ion irradiation is the rapid accumulation of end of life doses over a short duration.. Conversley, neutron irradiation experiments in thermal test reactors may accumulate damage at a rate of 3–5 dpa year, e.g. the ANSTO OPAL reactor with 20 MW is capable of 100 MeV with reactor face neutron thermal flux of 4.0E10 n/cm2/s thus resulting in a less than optimal 2 dpa per year.
A key question still exits between the complementarity of neutron and ion irradiation with respect to the nature of damage, size, density and distribution of dislocation loops; black dots; and the extent of the dislocation networks. Although the same number of displacements can be produced using ion irradiation, there are differences in spatial defect distribution between thes e teh two. The post-irradiation measurements in effect quantify the final state of damage and the neutron-ion equivalence without an evaluation of the damage path.
The simulation code Stopping and Range of Ions in Materials (SRIM) is used to model the irradiation process and compute the initial required experimental flux. Post irradiation studies of the micromechanical behaviour are done through nano-indentation (to a depth of 300 nm) using a diamond Berkovich tip. This allows for estimates of moduli and relative estimates of the strengths and hardening of individual phases and individual grains within a multiphase alloy. The results show a marked increase in the hardening of AA 6061 with a more modest increase in the Duplex steel 2205. Coupling these results to micromechanical FEA and crystal plasticity modelling, the authors hope to better describe the role of multi-scale modelling in complementing micromechanical testing and the extrapolation of results for engineering assessment
Aerosol iron solubility: comparison between the Australian subtropics and Southern ocean
No full textPast changes in the atmospheric deposition of soluble, or bioavailable, trace metals to high nutrient low chlorophyll (HNLC) and nitrogen replete tropical waters have been shown to modulate primary production, atmospheric CO2, and global climate. The deposition of soluble trace metals can also trigger toxic algal blooms, which impact Australia’s fisheries and coral reefs. An understanding of the sources (e.g. mineral dust and biomass emissions) and geochemistry of soluble trace metals in atmospheric aerosols is critical for determining the impact of trace metal deposition on ocean fertility in the past and the future. However, to date no trace metal solubility data exists for biomass emissions from Australian fires and there are very few estimates of soluble trace metal aerosols entering the Southern Ocean. Trace metal clean aerosols were collected during the early‐late dry season experiment at Gunn Point, Northern Territory to investigate the trace metal aerosol solubility associated with biomass burning. Previous studies have suggested that mineral dust is the dominant source of trace metal aerosol. However, mineral dust is relatively insoluble and a significant fraction of soluble trace metals in the atmosphere could originate from biomass burning rather than mineral dust. Here we use the combination of soluble aerosol chemistry, back trajectories and diurnal and advective radon components to identify trace metal source regions throughout the campaign duration. We compare aerosol iron solubility at Gunn Point in the subtropics, where biomass burning can dominate the aerosol load in the dry season, to iron solubility in baseline air at Cape Grim which is representative of the Southern Hemisphere background. In doing this we highlight the importance of aerosol source at different latitudes for the solubility and bioavailability of trace metals
Bardoxolone methyl prevents insulin resistance and the development of hepatic steatosis in mice fed a high-fat diet
No full textHigh-fat (HF) diet-induced obesity is a major risk factor for the development of insulin resistance and hepatic steatosis. We examined the hypothesis that bardoxolone methyl (BM) would prevent the development of insulin resistance and hepatic steatosis in mice fed a HF diet. C57BL/6J male mice were fed a lab chow (LC), HF (40% fat), or HF diet supplemented with 10 mg/kg/day BM orally for 21 weeks. Glucose metabolism was assessed using a glucose tolerance test (GTT) and insulin sensitivity test (IST). Signalling molecules involved in insulin resistance, inflammation, and lipid metabolism were examined in liver tissue via western blotting and RT-PCR. BM prevented HF diet-induced insulin resistance and alterations in the protein levels of protein tyrosine phosphatase 1B (PTP1B), forkhead box protein O1 (FOXO1) and BDNF, and expression of the insulin receptor (IR), IRS-1 and glucose-6-phosphatase (G6Pase) genes. Furthermore, BM prevented fat accumulation in the liver and decreases in the β-oxidation gene, peroxisomal acyl-coenzyme A oxidase 1 (ACOX) in mice fed a HF diet. In the livers of HF fed mice, BM administration prevented HF diet-induced macrophage infiltration, inflammation as indicated by reduced IL-6 and signal transducer and activator of transcription 3 (STAT3) protein levels and TNFα mRNA expression, and increased nuclear factor-like 2 (Nrf2) mRNA expression and nuclear protein levels. These findings suggest that BM prevents HF diet induced insulin resistance and the development of hepatic steatosis in mice fed a chronic HF diet through modulation of molecules involved in insulin signalling, lipid metabolism and inflammation in the liver.© 2015, Elsevier Ireland Ltd
Chemical and isotopic signatures of waters associated with the carbonation of ultramafic mine tailings, Woodsreef Asbestos Mine, Australia
No full textExtensive carbonate crusts have formed on the tailings of the Woodsreef Asbestos Mine, sequestering significant amounts of CO2 directly from the atmosphere. The physico-chemical (pH, T, conductivity), chemical (cations, dissolved inorganic carbon (DIC)) and isotopic (δ2H, δ18O, δ13CDIC, F14C) signatures of waters interacting with the tailings and associated carbonate precipitates provide insight into the processes controlling carbonation. We observe two distinct evolutionary pathways for a set of stream and meteoric-derived water samples, respectively, with both groups generally being characterised as moderately alkaline, bicarbonate-dominated and Mg-rich waters. Stream water samples are supersaturated with CO2 and therefore prone to degassing, which, in combination with evaporation, drives carbonate supersaturation and precipitation. Isotopic signatures indicate soil CO2 as the main carbon source in the stream waters entering the tailings pile, whereas water emerging downstream of the tailings pile may also contain carbon from the dissolution of isotopically light bedrock magnesite in an open system with respect to soil CO2. The evolution of meteoric-derived waters on the other hand, partly occurs under CO2-limited conditions, which results from reduced CO2 ingress at depth and/or a temporal lag between fluid alkalisation and kinetically hindered uptake of CO2 into alkaline solution. A high pH, Mg-rich meteoric water absorbs atmospheric CO2 after discharging into a tunnel within the tailings pile, resulting in high DIC concentrations with atmospheric carbon isotope signature. Evaporation of the water at the discharge point in the tunnel drives precipitation of hydromagnesite (Mg5(CO3)4(OH)2·4H2O), displaying a clear atmospheric isotope signature, broadly consistent with previous estimates of carbon and oxygen isotope fractionation during precipitation of hydrated Mg-carbonate. © 2016, Elsevier B.V
Cultural innovation and megafauna interaction in the early settlement of arid Australia
No full textElucidating the material culture of early people in arid Australia and the nature of their environmental interactions is essential for understanding the adaptability of populations and the potential causes of megafaunal extinctions 50–40 thousand years ago (ka). Humans colonized the continent by 50 ka1, 2, but an apparent lack of cultural innovations compared to people in Europe and Africa3, 4 has been deemed a barrier to early settlement in the extensive arid zone2, 3. Here we present evidence from Warratyi rock shelter in the southern interior that shows that humans occupied arid Australia by around 49 ka, 10 thousand years (kyr) earlier than previously reported2. The site preserves the only reliably dated, stratified evidence of extinct Australian megafauna5, 6, including the giant marsupial Diprotodon optatum, alongside artefacts more than 46 kyr old. We also report on the earliest-known use of ochre in Australia and Southeast Asia (at or before 49–46 ka), gypsum pigment (40–33 ka), bone tools (40–38 ka), hafted tools (38–35 ka), and backed artefacts (30–24 ka), each up to 10 kyr older than any other known occurrence7, 8. Thus, our evidence shows that people not only settled in the arid interior within a few millennia of entering the continent9, but also developed key technologies much earlier than previously recorded for Australia and Southeast Asia. © 2016, Nature Publishing Group
How old is the Tasmanian cultural landscape? A test of landscape openness using quantitative land-cover reconstructions
No full textAim
To test competing hypotheses about the timing and extent of Holocene landscape opening using pollen-based quantitative land-cover estimates.
Location
Dove Lake, Tasmanian Wilderness World Heritage Area, Australia.
Methods
Fossil pollen data were incorporated into pollen dispersal models and corrected for differences in pollen productivity among key plant taxa. Mechanistic models (REVEALS—Regional Estimates of VEgetation Abundance from Large Sites) employing different models for pollen dispersal (Gaussian plume and Lagrangian stochastic models) were evaluated and applied in the Southern Hemisphere for the first time.
Results
Validation of the REVEALS model with vegetation cover data suggests an overall better performance of the Lagrangian stochastic model. Regional land-cover estimates for forest and non-forest plant taxa show persistent landscape openness throughout the Holocene (average landscape openness ~50%). Gymnoschoenus sphaerocephalus, an indicator of moorland vegetation, shows higher values during the early Holocene (11.7–9 ka) and declines slightly through the mid-Holocene (9–4.5 ka) during a phase of partial landscape afforestation. Rain forest cover reduced (from ~40% to ~20%) during the period between 4.2–3.5 ka.
Main conclusions
Pollen percentages severely under-represent landscape openness in western Tasmania and this bias has fostered an over-estimation of Holocene forest cover from pollen data. Treeless vegetation dominated Holocene landscapes of the Dove Lake area, allowing us to reject models of landscape evolution that invoke late-Holocene replacement of a rain forest-dominated landscape by moorland. Instead, we confirm a model of Late Pleistocene inheritance of open vegetation. Rapid forest decline occurred after c. 4 ka, likely in response to regional moisture decline. © 2017 John Wiley & Sons Lt
Etching behavior of aluminum alloy extrusions
No full textThe etching treatment is an important process step in influencing the surface
quality of anodized aluminum alloy extrusions. The aim of etching is to produce
a homogeneously matte surface. However, in the etching process, further
surface imperfections can be generated on the extrusion surface due to uneven
materials loss from different microstructural components. These surface
imperfections formed prior to anodizing can significantly influence the surface
quality of the final anodized extrusion products. In this article, various factors
that influence the materials loss during alkaline etching of aluminum alloy
extrusions are investigated. The influencing variables considered include
etching process parameters, Fe-rich particles, Mg-Si precipitates, and extrusion
profiles. This study provides a basis for improving the surface quality in
industrial extrusion products by optimizing various process parameters. © 2014, The Minerals, Metals & Materials Society
Plant-microbe competition for nitrogen and phosphorous affected by drought
No full textCompetition for nutrients between plants and microbes is an important determinant for plant
growth, biodiversity and carbon cycling. Perturbations such as drought affect plant-microbe
competition for nitrogen (N) and phosphorus (P). Despite the importance of these nutrients in most
ecosystems, plant-microbe competition for N and P remains poorly understood. We used a novel
dual isotope labelling technique (15N and 32P) to assess plant-microbe competition for N and P
affected by drought in two different plant-soil systems.
Mesocosms were extracted from a grassland site where plants were strongly limited by N
(N-limiting system) and from a grassland site that showed strong soil P adsorption (P-adsorbing
system). Half of the mesocosms were subjected to drought one week prior to injection of the
tracers. Stable 15N (as KNO3) and radio-labelled 32P (as H3PO4) were injected, and measured in the
plant and microbial biomass 72 hrs later. Microbial uptake of 32P was strongly reduced by drought (on average by 89%), while
microbial 15N uptake was not. In contrast, drought reduced plant uptake of 15N (by 28%), but not of
32P. Microbial 15N uptake was much larger in the N-limiting system than in the P-adsorbing
system (by 491%), while plant 32P uptake was much larger in the P-adsorbing system than in the Nlimiting
system (by 703%). Both plants and microbes showed large flexibility in taking up 15N and
32P with the largest uptake of the nutrient that was in greatest demand.
Our results suggest that under drought conditions, plants lose in terms of N uptake, but win
in terms of P uptake when competing for these nutrients with microbes. These different
sensitivities to drought by plants and microbes may enhance decoupling of the N and P cycle with
increased drought conditions, depending on if plants and microbes are N or P limited
Antarctica at the global ‘Last Glacial Maximum’ – what can we learn from cosmogenic 10Be and 26Al exposure ages?.
No full textIce volume changes at the coastal margins of Antarctica during the global LGM are uncertain. The little evidence
available suggests that behaviour of the East and West Antarctic Ice Sheets are markedly different - and complex. It
is hypothesised that during interglacials, thinning of the Ross Ice Shelf, a more open-water environment and increased
precipitation, allowed outlet glaciers draining the Transantarctic Mnts and fed by interior Ice Sheets to advance
during moist warmer periods, out of phase with colder arid periods. In contrast, glacier dynamics along the vast
coastal perimeter of East Antarctica is strongly influenced by Southern Ocean conditions. Cosmogenic 10Be and
26Al chronologies, although restricted to ice-free ”oasis” and mountains flanking drainage glaciers, has become an
invaluable, if not unique, tool to quantify Pleistocene ice sheet variability. Despite major advances, extracting reliable
ages from glacial deposits in polar regions is problematic - recycling of previously exposed/ buried debris and continual
post-depositional modification leads to age ambiguities for a coeval glacial landform. More importantly, cold-based
ice advance can leave a landform unmodified resulting in young erratics deposited on ”ancient” bedrock. Exposure
ages from different localities throughout East Antarctica (Framnes Mnts, Lutzow-Holm Bay, Vestfold Hills) and West
Antarctica (Denton Ranges, Hatherton Glacier, Shackleton Range) highlight some of the new findings. This talk
presents results which quantify the magnitude and timing of paleo-ice sheet thickness changes, questions the validity
of an ”Antarctic LGM” and discusses the complexities presented by the geological spread observed in such studies
Whole-organism concentration ratios in wildlife inhabiting Australian uranium mining environments
No full textEnvironmental impact assessments conducted for Australian mine sites involving naturally occurring radioactive material require an assessment of radiation doses to wildlife. Whole-organism concentration ratios (CRwo) are pivotal in these assessments and previous reviews have identified a need for a more complete and consolidated database of Australian-specific CRwo that could be used. Concern had also been expressed by some stakeholders in Australia about the suitability of the default CRwo values provided in standard biota dose models (e.g., ERICA Tool, RESRAD-BIOTA, ICRP framework) for Australian wildlife and environmental conditions. In order to address these concerns and support the implementation of best-practice standards in environmental radiological assessment, the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA), with support from the Department of Resources, Energy and Tourism (RET), undertook an evaluation of existing data relating to wildlife inhabiting Australian uranium mining environments. CRwo values were calculated using data from a range of original sources. These included scientific journal publications, technical reports from Australian government organisations, site-specific data from mining operators and data from baseline environmental surveys undertaken during the 1970's and 1980's. The Australian data previously included in the international Wildlife Transfer Database (WTD, www.wildlifetransferdatabase.org) were also reviewed and updated. This paper discusses the data analysis process and associated uncertainties. CRwo values are reported for uranium, thorium, radium-226, lead-210 and polonium-210 for a range of endemic and introduced wildlife, with a focus on plants and animals from both terrestrial and freshwater environments where uranium mining has been proposed or undertaken. This has resulted in the calculation of more than 500 CRwo values for inclusion in the database. Australian-specific CRwo values will be compared to general values reported in the WTD including examples of specific wildlife groups or unique environmental conditions that are outside the range of the CRwo values in the WTD. Recommendations regarding biota types and environmental conditions for which data are most lacking will also be discussed. (authors)