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Quantification of residual stresses in multi-pass welds using neutron diffraction.
No full textNeutron diffraction results highlighted the effect of heat input through changes of travel speed and welding sequence (direction) on the residual stresses in multi-pass weldments of high strength low alloy steel. Residual stresses in excess of yield strength were developed in the weld metal and HAZ particularly for the upper-layers of welds which were not affected by the tempering of the subsequent weld layers. The magnitude of the residual stresses was significantly reduced by increasing the heat input. There was no substantial difference in the magnitude of the residual stresses when the direction of weld deposition was varied but the distribution was more uniform. © 2017 Elsevier B.V
Elemental contamination of an open-pit mining area in the Peruvian Andes
No full textNew technologies and higher prices of raw materials have promoted the expansion of mining activity throughout the world; if not properly regulated, this activity can lead to contamination of the local and regional environment. The city of Cerro de Pasco is located close to a large open-pit mine and in recent years, several reports have provided evidence of environmental contamination and related health problems. The aim of this paper is to evaluate the contamination in fluvial water, sediments and biological fluids from this area. The collective results show elevated metal and metalloid concentrations in rivers and sediments, especially in the areas downstream of the mine. For instance, Pb concentration in rivers downstream of the mine was 4.451 mg/L, while it was 0.037 mg/L upstream of the mine. Sediments also show higher concentration of metals and metalloids in the areas under the influence of the mine. Concentrations of elements in human blood were measured in the population of Paragsha, a village close to the mine. Analysis of the blood samples revealed elevated levels of metals and metalloids, particularly Pb, Cr, Al, Ni and Mn. All of the studied population showed blood concentrations of Al, Cr and Ni higher than those recommended by the WHO. The high concentration of elements found in the blood of the population could be related to the high concentration in the surrounding water sources, but further studies are required to determine the exact sources of exposure to these metals and metalloids. © 2014, Islamic Azad University (IAU)
Reply to comment by Karnauskas et al. on “Equatorial Pacific coral geochemical records show recent weakening of the Walker circulation”
No full textIn our paper describing a new coral record from Butaritari, we hypothesized that comparing the temporal trends in our records to coral records from farther east in the equatorial Pacific may support the evidence
for a weakening of a Walker circulation, documented elsewhere in the literature [Power and Smith, 2007; Tokinaga et al., 2012]. Weakening of the Walker circulation is expected under global warming due to an
imbalance in the rate of change in different aspects of the hydrological cycle [Vecchi and Soden, 2007]. We thank Karnauskas et al. [2015] for recognizing the value of our Butaritari coral climate reconstruction, and
we appreciate their critique of our study. The Karnauskas et al. [2015] analyses strengthen our argument regarding the utility of interisland coral-proxy derived sea surface temperature (SST) gradients as a Walker circulation metric, but we disagree with their interpretation of decadal variability in our records. Here we provide additional analyses, which confirm that our reconstruction [Carilli et al., 2014] shows a long-term weakening of the Walker circulation over 1972–1998. We also document that significant decadal variations in Walker circulation strength, and for particular choices of start and end years over which trends are calculated, are able to show slight Walker strengthening. Overall, we conclude that Walker circulation variations are more nuanced than either our original publication [Carilli et al., 2014] or the subsequent Karnauskas et al. [2015] comment would suggest. Karnauskas et al. [2015] also provide a detailed analysis of Equatorial Undercurrent (EUC) activity near the Gilbert Islands and argue that the EUC does not strongly affect Butaritari. Our original publication did not claim to find significant EUC/Butaritari linkages, and we appreciate the diligence of Karnauskas et al. [2015] for ruling this out as a possibility. © 2015, American Geophysical Union
PM2.5 and aerosol black carbon in Suva, Fiji
No full textConcentrations of particulate air pollution in Suva, Fiji, have been largely unknown and consequently, current strategies to reduce health risk from air pollution in Suva are not targeted effectively. This lack of air quality data is common across the Pacific Island Countries. A monitoring study, during 2014 and 2015, has characterised the fine particulate air quality in Suva, representing the most detailed study to date of fine aerosol air pollutants for the Pacific Islands; with sampling at City, Residential (Kinoya) and Background (Suva Point) sites. Meteorology for Suva, as it relates to pollutant dispersion for this period of time, has also been analysed. The study design enables the contribution of maritime air and the anthropogenic emissions to be carefully distinguished from each other and separately characterised. Back trajectory calculations show that a packet of air sampled at the Suva City site has typically travelled 724 km in the 24-h prior to sampling, mainly over open ocean waters; inferring that pollutants would also be rapidly transported away from Suva. For fine particulates, Suva City reported a mid-week PM2.5 of 8.6 ± 0.4 μg/m3, averaged over 13-months of gravimetric sampling. Continuous monitoring (Osiris laser photometer) suggests that some areas of Suva may experience levels exceeding the WHO PM2.5 guideline of 10 μg/m3, however, compared to other countries, Fiji's PM2.5 is low. Peak aerosol particulate levels, at all sites, were experienced at night-time, when atmospheric conditions were least favourable to dispersion of air pollutants. Suva's average ambient concentrations of black carbon in PM2.5, 2.2 ± 0.1 μg/m3, are, however, similar to those measured in much larger cities. With any given parcel of air spending only seven minutes, on average, over the land area of Suva Peninsula, these black carbon concentrations are indicative that significant combustion emissions occur within Suva. Many other communities in the Pacific Islands, as well as in Africa, Asia and South America share similar climate and similar burning practices and as such are likely to experience similar aerosol black carbon loadings. These black carbon levels indicate the need for combustion emissions, particularly those from open burning and diesel usage, to be addressed in air policy.© 2016, Elsevier Ltd
An in situ study of NiTi Powder Sintering using neutron diffraction
Get PDFThis study investigates phase transformation and mechanical properties of porous NiTi alloys using two different powder compacts (i.e., Ni/Ti and Ni/TiH2) by a conventional press-and-sinter means. The compacted powder mixtures were sintered in vacuum at a final temperature of 1373 K. The phase evolution was performed by in situ neutron diffraction upon sintering and cooling. The predominant phase identified in all the produced porous NiTi alloys after being sintered at 1373 K is B2 NiTi phase with the presence of other minor phases. It is found that dehydrogenation of TiH2 significantly affects the sintering behavior and resultant microstructure. In comparison to the Ni/Ti compact, dehydrogenation occurring in the Ni/TiH2 compact leads to less densification, yet higher chemical homogenization, after high temperature sintering but not in the case of low temperature sintering. Moreover, there is a direct evidence of the eutectoid decomposition of NiTi at ca. 847 and 823 K for Ni/Ti and Ni/TiH2, respectively, during furnace cooling. The static and cyclic stress-strain behaviors of the porous NiTi alloys made from the Ni/Ti and Ni/TiH2 compacts were also investigated. As compared with the Ni/Ti sintered samples, the samplessintered from the Ni/TiH2 compact exhibited a much higher porosity, a higher close-to-total porosity, a larger pore size and lower tensile and compressive fracture strength. © 1996-2020 MDP
Using neutron powder diffraction and first-principles calculations to understand the working mechanisms of porous coordination polymer sorbents
No full textMetal-organic frameworks (MOFs) are promising solid sorbents, showing gas selectivity and uptake capacities relevant to many important applications, notably in the energy sector. To improve and tailor the sorption properties of these materials for such applications, it is necessary to gain an understanding of their working mechanisms at the atomic and molecular scale. Specifically, it is important to understand how features such as framework porosity, topology, chemical functionality and flexibility underpin sorbent behaviour and performance. Such information is obtained through interrogation of structure-function relationships, with neutron powder diffraction (NPD) being a particularly powerful characterization tool. The combination of NPD with first-principles density functional theory (DFT) calculations enables a deep understanding of the sorption mechanisms, and the resulting insights can direct the future development of MOF sorbents. In this paper, experimental approaches and investigations of two example MOFs are summarized, which demonstrate the type of information and the understanding into their functional mechanisms that can be gained. Such information is critical to the strategic design of new materials with targeted gas-sorption properties. Copyright © International Union of Crystallograph
Application of a soil model in the numerical analysis of landmine interaction with protective structures
No full textBlast analysis using numerical techniques has become increasingly relevant to
anticipate the material response of protective structures. Improvised explosive devices and land mines pose a significant threat to the occupants of armoured vehicles, it’s therefore
important to increase the accuracy of the numerical analysis by incorporating more
sophisticated material models whilst maintaining mathematical tractability. The current
research employs an Arbitrary Lagrangian Eulerian (ALE) numerical technique in the
hydrocode LS-DYNA for the analysis of the blast event. Further, incorporation of a soil
model was carried out for the analysis of a TNT mine blast on a mild steel plate. The primary goals of the research are the implementation of an appropriate soil model and the use of multi-physics finite element analysis to model fluid structure interaction. The agreement with
experimental result is very good and the methodology employed captured some important
aspects of the blast-structure interaction
Radiation hardness of n-type SiC Schottky diodes
No full textThe results of recent IBIC and DLTS studies of radation damage in silicon carbide (SiC) diodes will be presented. n-type Schottky diodes prepared on an epitaxial grown 4H-SiC thin wafers have been irradiated by a raster scanned alpha particle microbeam (2 & 4 MeV He2+ ions separately) in order to create patterned damage structures at different depths within sensitive volume of tested diodes suitable for Ion Beam Induced Current (IBIC) microscopy. Deep level transient spectroscopy (DLTS) was used to characterize defects created in SiC after implantation of single alpha particles. Robust and proven IBIC experimental protocol [1] has been used to determine a degradation of the charge collection efficiency over a wide fluence range of damaging alpha particle. The radiation hardness of these SiC wafers is compared with the hardness of n-type silicon wafers grown by the Floating zone and Czochralski methods obtained by the same experimental protocol. A suitability of as prepared SiC diodes for the light ion detection and spectroscopy in the MeV range will be discussed from the perspecetive of applications in harsh radiation environments
Radon vertical profiles during the morning transition period
No full textVertical profiles and suitably-conditioned surface time histories of the natural radioactive noble gas radon-222 (radon) have long been demonstrated to be useful as quantitative indicators of diurnal- to synoptic-scale mixing processes within the continental lower troposphere. Radon’s well-characterised and slowly-varying source function over (ice-free)terrestrial surfaces, together with its short half-life of 3.8 days, makes it a particularly suitable passive scalar for the evaluation of boundary layer and convective mixing parameterisation schemes in a range of regional and global climate and pollution transport models. We provide a brief overview of ANSTO measurement programs using radon to characterise vertical mixing in the lower atmosphere, together with examples of their applications in modelling and pollution studies. We then present preliminary results from recent field campaigns collecting high resolution vertical radon profiles in the terrestrial boundary layer over rural New South Wales, using a radon sampler mounted on an instrumented motor-glider. The flights were conducted in the lowest 1000m of the atmosphere and, together with simultaneous ground-based and tower measurements, document the dispersion of radon emissions accumulated below the nocturnal stable inversion into the developing daytime convective boundary layer during the important morning transition period
The climate reconstruction potential of Acacia cambagei (gidgee) for semi-arid regions of Australia using stable isotopes and elemental abundances
No full textTo provide multi-centennial, annually-resolved records of climate for arid and semi-arid areas of Australia it is necessary to investigate the potential climate signals in tree species in this large region. Using a stable isotope and x-ray fluorescence approach to dendrochronology in Acacia cambagei, this study demonstrates short (10 years) proxies of temperature and precipitation are possible. Because rings in A. cambagei are difficult to see, precluding traditional dendrochronology, we used elemental abundances of Ca and Sr as an annual chronometer back to 1962. Radiocarbon analysis confirmed that our dating of wood from two trees. We compared δ13C and δ18O from the α-cellulose of the dated wood over the most recent 10 years (n = 10) to local climate records demonstrating significant relationships between δ18O and precipitation (r = −0.85, p < 0.002); mean monthly maximum temperature (r = 0.69, p < 0.03); and drought indexes (CRU scPDSI 0.5°, r = −0.89, p < 0.001) for February and March. Acacia cambagei may be useful in developing regional networks of climate proxies for drought. Using modern trees, in combination with architectural timbers, it may be possible to construct a multi-century, annually-resolved proxy-record of rainfall and temperature for semi-arid north-eastern Australia. © 2016 Elsevier Ltd