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Effect of scan rotation on the microstructure development and mechanical properties of 316L parts produced by laser powder bed fusion
No full textAdditive manufacturing possesses appealing features for producing high-performance components, for a wide range of materials. One of these features is the ability to locally tailor the microstructure and in turn, the mechanical properties. This study investigates how the microstructure of stainless steel 316L parts produced by laser powder bed fusion are affected by alternating the laser scan orientation. The microstructure consists of large elongated grains with a fine cell substructure. This study established the correlation between the orientation of this substructure and the crystallographic orientation. The results show that by producing parts without any rotation a quite unique crystallographic orientation can be achieved. The grain structure primarily consisted of large 〈101〉 oriented grains, that were separated by thin bands of small 〈100〉 oriented grains with respect to the building direction. As rotation was added these bands were eliminated. Samples that were produced without any rotation generated the highest tensile strength (527 ± 5.4 MPa), yield strength (449 ± 2.4 MPa) and ductility (58 ± 1.3%). The lowest mechanical properties were obtained for samples that were produced using a scan rotation of 67° with the tensile strength of 485 ± 4.8 MPa, yield strength of 427 ± 5.4 MPa and ductility of 50 ± 1.3%. This indicates that cell orientation and crystallographic orientation plays an essential role in the tensile properties of 316L parts produced by laser powder bed fusion (L-PBF). © 2020 Elsevier Inc
Mapping of Elemental Composition in Air-Oxidized Ti3SiC2
No full textDepth-profiling of elemental composition at the near surface of air-oxidized Ti3SiC2 was studied by secondary ion mass spectrometry (SIMS). The duplex microstructure of oxides formed at air-oxidized Ti3SiC2 surface was observed which consisted of an outer uniform layer of rutile-TiO2 and an inner graded layer of TiO2 and SiO2. The thickness of oxide scales increased with an increase in temperature. Ti3SiC2 is resistant to oxidation in air at up to 1100 degrees C. Copyright © 2008 Australian Ceramic Society.This article is not available in electronic format, it is only available in print. The Journal of the Australian Ceramic Society is held by ANSTO Library where a copy of the article can be accessed
Radiochemistry on chip: towards dose-on-demand synthesis of PET radiopharmaceuticals
No full textAbstractWe have developed an integrated microfluidic platform for producing 2-[18F]-fluoro-2-deoxy-D-glucose (18F-FDG) in continuous flow from a single bolus of radioactive isotope solution, with constant product yields achieved throughout the operation that were comparable to those reported for commercially available vessel-based synthesisers (40–80%). The system would allow researchers to obtain radiopharmaceuticals in a dose-on-demand setting within a few minutes. The flexible architecture of the platform, based on a modular design, can potentially be applied to the synthesis of other radiotracers that require a two-step synthetic approach, and may be adaptable to more complex synthetic routes by implementing additional modules. It can therefore be employed for standard synthesis protocols as well as for research and development of new radiopharmaceuticals. © 2013 The Royal Society of Chemistr
Intrinsic microtubule GTP-cap dynamics in semi-confined systems: kinetochore–microtubule interface
No full textIn order to quantify the intrinsic dynamics associated with the tip of a GTP-cap under semi-confined conditions, such as those within a neuronal cone and at a kinetochore–microtubule interface, we propose a novel quantitative concept of critical nano local GTP-tubulin concentration (CNLC). A simulation of a rate constant of GTP-tubulin hydrolysis, under varying conditions based on this concept, generates results in the range of 0-420 s−1. These results are in agreement with published experimental data, validating our model. The major outcome of this model is the prediction of 11 random and distinct outbursts of GTP hydrolysis per single layer of a GTP-cap. GTP hydrolysis is accompanied by an energy release and the formation of discrete expanding zones, built by less-stable, skewed GDP-tubulin subunits. We suggest that the front of these expanding zones within the walls of the microtubule represent soliton-like movements of local deformation triggered by energy released from an outburst of hydrolysis. We propose that these solitons might be helpful in addressing a long-standing question relating to the mechanism underlying how GTP-tubulin hydrolysis controls dynamic instability. This result strongly supports the prediction that large conformational movements in tubulin subunits, termed dynamic transitions, occur as a result of the conversion of chemical energy that is triggered by GTP hydrolysis (Satarić et al., Electromagn Biol Med 24:255–264, 2005). Although simple, the concept of CNLC enables the formulation of a rationale to explain the intrinsic nature of the “push-and-pull” mechanism associated with a kinetochore–microtubule complex. In addition, the capacity of the microtubule wall to produce and mediate localized spatio-temporal excitations, i.e., soliton-like bursts of energy coupled with an abundance of microtubules in dendritic spines supports the hypothesis that microtubule dynamics may underlie neural information processing including neurocomputation. © 2012, Springer Natur
Radon: a universal baseline indicator at sites with contrasting physical settings
Full text linkThe primary goal of World Meteorological Organisation Global Atmosphere Watch (WMO‐GAW) baseline stations is systematic global monitoring of chemical composition of the atmosphere, requiring a reliable, consistent and unambiguous approach for the identification of baseline air. Premier stations in the GAW baseline network span a
broad range of physical settings, from remote marine to high‐altitude continental sites, necessitating carefully tailored
site‐specific requirements for baseline sampling, data selection, and analysis. Radon‐222 is a versatile and unambiguous terrestrial tracer, widely‐used in transport and mixing studies. Since the majority of anthropogenic pollution sources also have terrestrial origins, radon has become a popular addition to the ‘baseline selection
toolkit’ at numerous GAW stations as a proxy for ‘pollution potential’. In the past, detector performance and postprocessing
methods necessitated the adoption of a relaxed (e.g. 100 mBq m‐3) radon threshold for minimal terrestrial influence, intended to be used in conjunction with other baseline criteria and analysis procedures, including wind speed, wind direction, particle number, outlier rejection and filtering. However, recent improvements in detector sensitivity, stability and post‐processing procedures have reduced detection limits below 10 mBq m‐3 at Cape Grim and to 25 mBq m‐3 at other baseline stations. Consequently, for suitably sensitive instruments (such as the ANSTO designed and built two‐filter dual‐flow‐loop detectors), radon concentrations alone can be used to unambiguously identify air masses that have been removed from terrestrial sources (at altitude or over ice), or in equilibrium
with the ocean surface, for periods of >2‐3 weeks (radon ≤ 40 mBq m‐3). Potentially, radon observations alone can thus provide a consistent and universal (site independent) means for baseline identification. Furthermore, for continental sites with complex topography and meteorology, where true ‘baseline’ conditions may never
occur, radon can be used to indicate the least terrestrially‐perturbed air masses, and provide a means by which to apply limits to the level of ‘acceptable terrestrial influence’ for a given application. We demonstrate the efficacy of the radon‐based selection at a range of sites in contrasting physical settings, including: Cape Grim (Tasmania), Cape Point (South Africa), Mauna Loa (Hawaii), Jungfraujoch (Switzerland) and Schneefernerhaus (Germany).Bureau of Meteorology and CSIRO Oceans and Atmosphere,Climate Science Centre
Synthesis and stability of S-(2-[18F]fluoroethyl)-L-homocysteine for potential tumour imaging
No full textinThe F-18 labelled methionine derivative S-(2-[18F]fluoroethyl)-L-homocysteine ([18F]FEHCys) was prepared by a one-pot two-step synthesis via the protected S-(2-bromoethyl)-L-homocysteine 1 and S-(2-chloroethyl)-L-homocysteine 2 precursors. The bromoethyl derivative 1 gave higher radiochemical yields (40% at 5 min) at 100°C compared with the chloro-analogue (22% at 100°C in 30 min). However, [18F]FEHCys was found to be unstable in aqueous systems being transformed to the corresponding hydroxyl derivative within 20 min. © 2008 John Wiley & Sons, Ltd
Synthesis of 1,4-triazole linked zanamivir dimers as highly potent inhibitors of influenza A and B
No full textThe copper catalyzed azide alkyne cycloaddition (CuAAC) reaction – the quintessential ‘click’ reaction – was used to synthesise dimers of the neuraminidase inhibitor zanamivir in high yields. The effect upon anti-viral activity of varying the linker length and the number of triazole units was explored. All dimers were tested for anti-viral activity against influenza A/Sydney/5/97 and B/Harbin/7/94 in a cytopathic effect (CPE) assay. © Royal Society of Chemistr
Export production in the New-Zealand region since the last glacial maximum
No full textIncreased export production (EP) in the Subantarctic Zone (SAZ) of the Southern Ocean due to iron fertilisation has been proposed as a key mechanism for explaining carbon drawdown during the last glacial maximum (LGM). This work reconstructs marine EP since the LGM at four sites around New Zealand. For the first time in this region, 230-Thorium-normalised fluxes of biogenic opal, carbonate, excess barium, and organic carbon are presented. In Subtropical Waters and the SAZ, these flux variations show that EP has not changed markedly since the LGM. The only exception is a site currently north of the subtropical front. Here we suggest the subtropical front shifted over the core site between 18 and 12 ka, driving increased EP. To understand why EP remained mostly low and constant elsewhere, lithogenic fluxes at the four sites were measured to investigate changes in dust deposition. At all sites, lithogenic fluxes were greater during the LGM compared to the Holocene. The positive temporal correlation between the Antarctic dust record and lithogenic flux at a site in the Tasman Sea shows that regionally, increased dust deposition contributed to the high glacial lithogenic fluxes. Additionally, it is inferred that lithogenic material from erosion and glacier melting deposited on the Campbell Plateau during the deglaciation (18–12 ka). From these observations, it is proposed that even though increased glacial dust deposition may have relieved iron limitation within the SAZ around New Zealand, the availability of silicic acid limited diatom growth and thus any resultant increase in carbon export during the LGM. Therefore, silicic acid concentrations have remained low since the LGM. This result suggests that both silicic acid and iron co-limit EP in the SAZ around New Zealand, consistent with modern process studies. © 2017 Elsevier B.V
The 18 kDa translocator protein (peripheral benzodiazepine receptor) expression in the bone of normal, osteoprotegerin or low calcium diet treated mice
Full text linkThe presence of the translocator protein (TSPO), previously named as the mitochondrial or peripheral benzodiazepine receptor, in bone cells was studied in vitro and in situ using RT-qPCR, and receptor autoradiography using the selective TSPO ligand PK11195.
In vitro, the TSPO is highly expressed in osteoblastic and osteoclastic cells.
In situ, constitutive expression of TSPO is found in bone marrow and trabecular bone, e.g., spongiosa. Mice with a reduction of bone turnover induced by a 4-day treatment of osteoprotegerin reduces [3H]PK11195 binding in the spongiosa (320±128 Bq.mg−1, 499±106 Bq.mg−1 in saline-treated controls). In contrast, mice with an increase in bone turnover caused by a 4-day low calcium diet increases [3H]PK11195 binding in the spongiosa (615±90 Bq.mg−1).
Further, our study includes technical feasibility data on [18F]fluoride microPET imaging of rodent bone with altered turnover. Despite [18F]fluoride having high uptake, the in vivo signal differences were small. Using a phantom model, we describe the spillover effect and partial volume loss that affect the quantitative microPET imaging of the small bone structures in experimental mouse models.
In summary, we demonstrate the expression of TSPO in small rodent bone tissues, including osteoblasts and osteoclasts. A trend increase in TSPO expression was observed in the spongiosa from low to high bone turnover conditions. However, despite the potential utility of TSPO expression as an in vivo biomarker of bone turnover in experimental rodent models, our small animal PET imaging data using [18F]fluoride show that even under the condition of a good biological signal-to-noise ratio and high tracer uptake, the currently achievable instrument sensitivity and spatial resolution is unlikely to be sufficient to detect subtle differences in small structures, such as mouse bone. © 2012 Plos On
Rats with altered behaviour following nerve injury show evidence of centrally altered thyroid regulation
No full textThe co-morbidity of mood disturbance, in a proportion of patients, is now described across a wide range of chronic disease states. Similarly, a ‘Low Thyroid Syndrome’ is also reported in a proportion of individuals with chronic diseases. Here, we report on central changes in an animal model of inflammatory stress in which altered social behaviour, representing social disability, persists in a sub-group of rats following injury. We showed in an earlier study that rats with social disability following injury have significantly decreased peripheral thyroid hormones, with no increase in Thyroid Stimulating Hormone (TSH). Only rats identified by behavioural change showed changes in hypothalamic gene expression. In whole hypothalamus extracted RNA, relative expression of mRNA for Thyrotrophin-releasing hormone (TRH) was significantly down-regulated in disabled rats (p = 0.039) and deiodinase 3 up-regulated (p = 0.006) compared to controls. Specifically in the paraventricular nucleus (PVN), numbers of immunoreactive cells for deiodinase 3-like and thyroid hormone receptor beta-like proteins were decreased in the sub-group with disability compared to the control group (p = 0.031 and p = 0.011 respectively). In rats with behavioural change post-injury, down-regulation of TRH provides an explanation for the failure of the hypothalamo-pituitary-thyroid (HPT) axis to respond to the post-injury decrease in thyroxine. Decreased local expression of deiodinase 3 protein, resulting in a local increase in T3, offers an explanation for down regulation of TRH in the hypophysiotrophic TRH neurons. It is possible that, in a sub-group of animals identified behaviourally, a mechanism resulting in hypothalamic down-regulation of the HPT axis persists following inflammatory injury. © 2014 Elsevier B.V