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The formation of eutectic phases and hot cracks in one Ni–Mo–Cr superalloy.
No full textThe structure and the formation mechanism of brittle eutectic phases and hot cracks formed at grain boundaries were investigated in two Ni-Mo-Cr superalloys with different silicon contents (0.06 and 0.46 wt.%). The eutectic phases and hot cracks can be observed along the rolling direction in the 0.46 wt.% Si heat when heated to 1335 °C or a higher peak temperature up to 1365 °C. Exposure to the higher peak temperatures resulted in the formation of larger eutectic phases and hot cracks in the higher silicon heat. Conversely, there are fewer eutectic phases and smaller hot cracks forming in the low-silicon heat when heated to 1365 °C. The eutectic phases were identified as γ-M6C′ type. Based on the constitutional liquation theory and thermodynamic calculations, it was found that the formation of the eutectic phases and hot cracks is due to the localized melting of primary M6C carbides and surrounding Si-riched matrix. The degree of elements segregation in liquid films determines whether liquid films solidify into eutectic phases or cause hot cracks. This model can reasonably explain the observed phenomena and contribute to designing appropriate solid-solution treatment process and welding procedure to avoid brittle phases and cracks in the Ni-Mo-Cr superalloy. © 2015 Elsevier B. V
High-temperature corrosion of helium ion-irradiated Ni-based alloy in fluoride molten salt
No full textA comparison of the effect of helium-ion-radiation damage on a Ni–Mo–Cr–Fe alloy exposed to high-temperature (750 °C) corrosion in eutectic LiF–NaF–KF molten salt has been made. Microstructural examination showed that both the corroded-only and irradiated and corroded samples exhibit the characteristics of intergranular corrosion. However, helium ion irradiation introduces defects such as helium bubbles and cavities into the microstructure, greatly increasing intragranular corrosion of the irradiated sample. The thickness of the remaining corrosion zone for the irradiated sample was much greater than that for the unirradiated sample. © 2014 Elsevier Ltd
Late Holocene record of environmental changes, cyclones and tsunamis in a coastal lake, Mangaia, Cook Islands
No full textA 4.3 m-long peat sequence from the shore of Lake Tiriara, Mangaia, Cook Islands, was analyzed using an ITRAX core scanner equipped with a magnetic susceptibility meter. Variations in the elemental profiles, providing insights into long- and short-term environmental changes over the last 3500 years, are supported by grain size data and diatom assemblages. The scattering ratio (Mo Inc/Mo Coh) was evaluated and found to represent a good proxy for organic matter in peat. X-Ray Fluorescence (XRF) data were processed by principal component analysis that confirmed the distinction of biogenic and detrital phases, organic matter and elements of marine origin. The record preserved in the peat sequence includes a peatland infilling stage followed by alternating drier and wetter periods. A notable steady increase in clay associated with high counts of detrital elements from 2000–1700 cal yr BP is attributed to increased erosion, which is most probably linked with human colonization and/or more intense chemical weathering linked with a wetter climate. Freshwater gastropods (Melanoides sp.), which were possibly introduced by humans, or are native, occupied the wetland during a period of lower water level about 1000–1100 cal yr BP. Short-term changes in the elemental profiles are often linked with slight coarsening of the inorganic fraction that is, however, only revealed after grain size analysis. Peaks in marine indicators (Br, Cl, S, and/or Ca) associated with marine-dominated diatom assemblages most probably represent marine incursions through the underground tunnel in the makatea, a fossilized, uplifted coral limestone rim. While none of the marine event units present characteristics typical of cyclone or tsunami deposits, the concurrent or absent peak of detrital elements (Fe, Si, Rb, Ti, K) attributed to increased erosion of the volcanic cone associated with a cyclone is used to distinguish both types of events, as also suggested by principal component analysis. © 2016 John Wiley & Sons Australia, Lt
Screening assessment of dose rates to wildlife related to the Nuclear Medicine Mo99 Facility
Get PDFANSTO has performed a screening assessment on potential dose rates to environmental receptors (wildlife) associated with the planned ANSTO Nuclear Medicine (ANM) Mo99 Facility. The ANM facility will be located on the 50 hectare ANSTO Lucas Heights site, which is surrounded by a 1.6 km radius buffer zone owned by the Commonwealth or its Agencies. The buffer zone is used by humans for recreational purposes and is home to a range of plant and animal wildlife. During its routine operations in producing medical isotopes and performing research, ANSTO releases small amounts of radionuclides through stack emissions and, after testing, through liquid discharges to the public sewer system. The purpose of this assessment is to use a standard screening approach to determine if potential dose rates to local wildlife from future releases, including the ANM Mo99 Facility, are below international benchmarks.
The assessment used methods from international best practice as laid out by the ARPANSA Guide: Radiation Protection of the Environment, which is consistent with current approaches set forth by the International Commission on Radiological Protection (ICRP) and the International Atomic Energy Agency (IAEA). The screening evaluations considered exposure to a range of terrestrial organisms in the buffer zone from stack emissions via the air pathway, and, to a range of marine organisms near the ocean outlet at Potter Point, New South Wales via the liquid effluent pathway. Dose assessments were performed using the ERICA tool with radioactivity concentrations for air and water determined from data collected during routine monitoring of stack emissions and effluent releases at ANSTO. Concentration values along air and water pathways were overestimated, consistent with an approach of using conservative assumptions in this screening assessment.
In summary, despite using overestimates for radioactivity concentrations associated with ANSTO’s emissions, results indicate potential risk quotients that are below standard benchmarks for all organisms and all pathways considered. Dose rates to organisms were determined to be below the lowest benchmark for potential harmful effects (10 μGy hr-1). These results are consistent with previous studies in determining no significant impacts from ANSTO effluents. Therefore, potential radioactivity releases from the ANM Facility are unlikely to impact local wildlife. Although projected dose rates are low, the release of low levels of radionuclides in air and water discharges indicates the need for ongoing monitoring and periodic re-evaluation
The molecular mechanisms underpinning the therapeutic properties of oleanolic acid, its isomer and derivatives for type 2 diabetes and associated complications
No full textRecent research has uncovered the molecular mechanisms responsible for the therapeutic properties of oleanolic acid (OA), its isomer ursolic acid (UA), and derivatives. In particular, recent reports have highlighted the benefits of these compounds in the prevention and treatment of type 2 diabetes and associated life-threatening complications, such as nonalcoholic fatty liver disease, nephropathy, retinopathy, and atherosclerosis. The prevalence of type 2 diabetes is of major concern since it is reaching global epidemic levels. Treatments targeting the signaling pathways altered in type 2 diabetes are being actively investigated, and OA and UA in natural and derivative forms are potential candidates to modulate these pathways. We will explore the findings from in vitro and in vivo studies showing that these compounds: (i) improve insulin signaling and reduce hyperglycemia; (ii) reduce oxidative stress by upregulating anti-oxidants and; (iii) reduce inflammation by inhibiting proinflammatory signaling. We will discuss the molecular mechanisms underpinning these therapeutic properties in this review in order to provide a rationale for the future use of OA, UA, and their derivatives for the prevention and treatment of type 2 diabetes and associated comorbidities. © 1999-2020 John Wiley & Sons, Inc
DHA prevents altered 5-HT1A, 5-HT2A, CB1 and GABAA receptor binding densities in the brain of male rats fed a high-saturated-fat diet
No full textLow levels of docosahexaenoic acid (DHA) have been linked to a number of mental illnesses such as memory loss, depression and schizophrenia. While supplementation of DHA is beneficial in improving memory and cognition, the influence of dietary fats on the neurotransmitters and receptors involved in cognitive function is still not known. The aim of this study was to investigate serotonin receptor (5-HT(1A) and 5-HT2A), cannabinoid receptor (CB1) and gamma-aminobutyric acid type A (GABA(A)) receptor binding densities in the brain of male rats fed a high-saturated-fat (HF) diet, as well as the effect of DHA supplementation on HF diet. Alterations of these receptors in the post-mortem rat brain were detected by [(3)H]-WAY-100635, [(3)H]-ketanserin, [(3)H]-CP-55,940 and [(3)H]-muscimol binding autoradiography, respectively. In the hippocampus, the 5-HT(1A), CB1 and GABA(A) receptor binding densities significantly increased in response to an HF diet, while in the hypothalamus, 5-HT(1A) and CB1 binding densities significantly increased in HF-fed rats. Importantly, DHA supplementation prevented the HF-induced increase of receptors binding density in the hippocampus and hypothalamus. Furthermore, DHA supplementation attenuated 5-HT2A receptor binding density in the caudate putamen, anterior cingulate cortex and medial mammillary nucleus, which was also increased in HF group. This study showed that an HF diet increased 5-HT(1A), 5-HT2A, CB1 and GABA(A) receptor binding densities in the brain regions involved in cognitive function and that dietary DHA can attenuate such alterations. These findings provide insight into the mechanism by which DHA supplementation ameliorates reduced cognitive function associated with an HF diet. © 2013 Elsevier Inc
Special testing equipment and validation of measurement methodologies for high temperature low cycle fatigue testing of miniature metallic specimens
No full textA technique for high temperature low cycle fatigue testing of metallic materials has been developed, to determine fatigue behaviour through the testing of miniature specimens. The miniature specimen geometry was specifically designed, such that it could be manufactured from a small volume of material removed by chain-drilling extraction. An extensometry method to measure and control strain at the specimen shoulders during testing was adopted. This was undertaken to minimise the deleterious contact effects that can occur via extensometry attached at the gauge length of specimens, hence leading to premature failure and inaccurate fatigue data. By the application of this technique, the high temperature low cycle fatigue behaviour of 2.25Cr-1Mo steel was successfully characterised at 540 °C, under a fully reversed strain-controlled regime. The fatigue properties of the steel obtained from testing miniature specimens were shown to correlate well with existing literature for the material under comparable conditions, as determined by the testing of conventional standard-sized specimens. © 2016 Society for Experimental Mechanic
Sequestration of atmospheric CO2 in chrysotile mine tailings of the Woodsreef Asbestos Mine, Australia: Quantitative mineralogy, isotopic fingerprinting and carbonation rates
No full textSince closure of the Woodsreef Asbestos Mine, located in the Great Serpentinite Belt (GSB), New South Wales, Australia, extensive carbonate-rich crusts have formed by recessive weathering of fine-grained material on the surface of the tailings pile. A relationship exists between the mode of carbonate occurrence, the mineralogy and the isotopic fingerprint of carbonates from the tailings pile. Vertical carbonate crusts, covering most of the tailings, predominantly consist of the hydrated Mg-carbonate hydromagnesite (Mg5(CO3)4(OH)2·4H2O), which has precipitated from evaporating meteoric waters incorporating atmospheric CO2, as reflected in high δ18O, δ13C and F14C signatures, respectively. Low and variable concentrations of magnesite, dolomite and calcite represent bedrock carbonate, which has formed during alteration of the serpentinite bedrock before mining and is characterised by moderately high δ18O, low δ13C and F14C, a signature typical for ‘weathering-derived’ magnesite deposits in the GSB. The carbonate fraction of deep cement samples, collected from 70 to 120 cm below the surface, representing the bulk tailings material at depth, predominantly consists of pyroaurite (Mg6Fe2(CO3)(OH)16·4H2O) and, despite stable isotope signatures similar to bedrock, contains significant radiocarbon. This indicates that pyroaurite, forming under different conditions as hydromagnesite, may represent an additional trap for atmospheric CO2 in the Woodsreef mine tailings. The distribution of carbonates and quartz, together with the absence of isotopic mixing trends between bedrock carbonate and atmospheric-derived carbonate, strongly indicates that dissolution and re-precipitation of bedrock carbonate is not a dominant process in the Woodsreef tailings. The cations for carbonate formation are instead derived from the dissolution of serpentine minerals (lizardite and chrysotile) and brucite.
The internal standard method and the reference intensity method have been used with X-ray diffraction data to estimate the abundance of the two major carbonate minerals hydromagnesite and pyroaurite, respectively. Considering the formation of hydromagnesite on the outer surface of the tailings pile alone or together with formation of pyroaurite within the tailings pile we conclude that, between 1400 and 70,000 t of atmospheric CO2 have been sequestered in the mine tailings since closure of the mine 29 a ago. Carbonation rates of 27 g C m− 2 y− 1 and 1330 g C m− 2 y− 1 are significantly higher than background rates of CO2 uptake by chemical weathering and demonstrate the potential of passive carbonation of mine tailings as a cost and energy effective alternative for storage of CO2 in carbonate minerals. © 2013 Elsevier B.V
New pathway for the preparation of pyrochlore Nd2Zr2O7 nanoparticles
No full textPyrochlore Nd2Zr2O7 nanoparticles were prepared by complex-precipitation in aqueous media, followed by calcination in MgO matrix and subsequent dissolution processing. A suite of characterization techniques, including X-ray diffraction, Raman, TEM, SEM, dynamic light scattering, and nitrogen sorption, was employed to investigate the structure and particle size of the synthesized nano materials. Results show that calcination at 1200 °C for 20 h forms Nd2Zr2O7 with pyrochlore structure. The matrix phase (MgO) had no effect on the formation of pyrochlore phase. The MgO phase was readily removed by dissolution at 0.5 M HNO3 aqueous solution; and the remaining pyrochlore Nd2Zr2O7 nanoparticles had a diameter of approximately 200 nm estimated by TEM and approximately 550 nm determined by light scattering due to slight aggregation. The bulk density of the pelletized powder reached approximately 99% of theoretical value, after uniaxial pressing at 2.0–2.5 MPa and sintering at 1400 °C for 48 h. © 2015 Elsevier B.V
Radiotracer imaging studies in hepatic encephalopathy: ISHEN practice guidelines
No full textThere is lack of consensus on radiotracer usage in hepatic encephalopathy (HE). We have focused our attention on three main areas: (i) radiotracer imaging in animal models of HE, (ii) methodological issues of radiotracer imaging in HE and (iii) radiotracer imaging studies on the pathophysiology and (new) therapies in HE. We suggest the following: 1. Positron emission tomography (PET) and single photon emission computed tomography lend themselves to the study of animal models of HE, but the models that are suitable depend on the specific research question. Magnetic resonance imaging (MRI) may be a useful alternative technique. 2. Owing to the cost of the technique, there is a need for multicentre human PET studies to overcome the problem of underpowered small studies being undertaken in individual research centres. There should be a unified PET protocol with central, anonymised data analysis in one centre, using validated methodology, on behalf of all participating centres. Such studies would be useful for the assessment of early intervention in patients with subtle neuropsychiatric symptoms, or for clarification of the effect of liver transplantation on HE. 3. While radiotracer imaging modalities remain useful research tools for the study of pathogenesis and for the assessment of treatment effects, there is no consensus on the use of imaging in routine clinical practice for diagnosis and prognosis. The most promising objective tools appear to be magnetic resonance spectroscopy (MRS) and volumetric MRI, which can be performed in multiple centres without the difficulties that radiotracer imaging entail. © 2009 John Wiley & Sons A/