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Irradiation behaviour of α2 and γ phases in He ion implanted titanium aluminide alloy
No full textA Ti–45Al–2Nb–2Mn + 0.8 vol.% TiB2 (at.%) alloy with fully lamellar microstructure consisting of hexagonal-close-packed (hcp) α2 and face-centred-tetragonal (fct) γ phases was irradiated by implanting helium ions to different fluences. Microstructural examination showed that helium cavities are formed in both the α2 and γ phases after He-ion irradiation. However, the helium cavities and their size change with fluence are much larger in the α2 phase than those in the γ phase, indicating that the γ phase exhibits better tolerance to the He-ion irradiation than the α2 phase. Since α2 and γ phases have different crystal structures, they possess differences in helium solubility and interstitial migration. These differences are responsible for the variation in radiation damage behaviour between the two phases. © 2014, Elsevier Ltd
Segregation-Induced Low-Dimensional Surface Structures in Oxide Semiconductors
No full textThe present work considers quasi-isolated low-dimensional surface structures, which are formed as a result of segregation of intrinsic and extrinsic defects in oxide semiconductors. It has been documented that the local properties of these structures, such as crystalline structure, electronic structure, chemical composition, as well as charge and mass transport kinetics, are entirely different from those of the bulk phase. There is an increasingly urgent need to better understand their local properties, which have a strong impact on the reactivity of solids in general and photocatalytic properties in particular. The accumulation of data on the properties of surface structures opens a new discipline of the science of materials interfaces. The present work is focused on the surface structures, which are formed at TiO2-based semiconductors. It is shown that these structures play crucial role in the conversion of solar energy into chemical energy. © 2014, Springer-Verlag Berlin Heidelberg
Lidar investigation of infiltration water heterogeneity in the Tamala Limestone
Get PDFTo better manage groundwater resources in carbonate areas and improve our understanding of speleothem archives, it is important to understand and predict unsaturated zone hydrology in karst. The high level of complexity and spatial heterogeneity of such systems is challenging and requires knowledge of the typical geometry of karstic features. We present an exhaustive characterization of Golgotha Cave, SW Western Australia, based on an extensive LIDAR measurement campaign. The cave is developed in Quaternary age aeolianite (dune limestone) and contains speleothem records. We collect 30 representative 3D scan images from this site using FARO Focus3D, a high-speed 3D laser scanner, to visualize, study and extract 2D and 3D information from various points of view and at different scales. In addition to LIDAR data, 32 automatic drip loggers are installed at this site to measure the distribution and volume of water flow. We perform mathematical morphological analyses on the cave ceiling, to determine statistical information regarding the stalactites widths, lengths and spatial distribution. We determine a relationship between stalactites diameter and length. We perform tests for randomness to investigate the relationship between stalactite distribution and ceiling features such as fractures and apply this to identify different types of possible flow patterns such as fracture flow, solution pipe flow, primary matrix flow etc. We also relate stalactites density variation with topography of the cave ceiling which shows hydraulic gradient deviations. Finally we use Image Quilting, one of the recently developed multiple-point geostatistics methods, with the training images derived from LIDAR data to create a larger cave system to represent not only the caves that are visible, but the entire system which is inaccessible. As a result, an integral geological model is generated which may allow other scientists, geologist, to work on two different levels, integrating different speleothem datasets: (1) a basic level based on the accurate and metric support provided by the laser scanner; and (2) an advanced level using the image-based modelling
Electric-field-induced phase transitions in co-doped Pb(Zr1−xTix)O3 at the morphotropic phase boundary
No full textThe strain- and polarization-electric field behavior was characterized at room temperature for Pb0.98Ba0.01(Zr1−xTix)0.98Nb0.02O3, 0.40 x 0.60. The investigated compositions were located in the vicinity of the morphotropic phase boundary, giving insight into the influence of crystal structure on the hysteretic ferroelectric behavior. The remanent strain of particular compositions is shown to be larger than theoretically allowed by ferroelectric switching alone, indicating the presence of additional remanent strain mechanisms. A phenomenological free energy analysis was used to simulate the effect of an applied electric field on the initial equilibrium phase. It is shown that electric-field-induced phase transitions in polycrystalline ferroelectrics can account for the experimental observations. The experimental and simulation results are contrasted to neutron diffraction measurements performed on representative compositions in the virgin and remanent states. © 2014, National Institute for Materials Science
Geoelectrical characterization of hydrological processes in a buried braided river system
No full textThe Macquarie Marshes (NSW, Australia) cover approximately 200 square km of the Macquarie River flood-plains. The marshes are one of the largest remaining inland semi-permanent wetlands in southeastern Australia. Diversity of fauna and flora has decreased in the wetlands while the flood-drought cycles controlling these ecosystems have been affected by recent human activity. An Electrical Resistivity Tomography survey has been carried out to provide insight into the surface water/ groundwater interactions occurring at the north-western part of the marshes and to identify potential recharge areas of the aquifer systems. In the resistivity sections three main units can be identified: 1. A top unit of low-resistivity (1 to 6 ohm.m) with about 5 meter thick on average. 2. A middle unit of higher electrical resistivity (6 to 20 ohm.m) that continues to a depth of approximately 20 metres and is discontinuous laterally. 3. A bottom unit below a depth of 20 to 25 metres with resistivity decreasing to values similar to those of the top unit. The resistivity results has allowed to identify clay dominated and sand dominated materials. The groundwater is recharged from surface water following sandy windows in the clay created by modern channels on the surface of the marshes.© European Association of Geoscientists & Engineers
Modelling of biota dose effects, Report of working group 6 of EMRAS II programme
No full textRadiological protection of the environment is advancing from the old paradigm which stated that if humans are protected then by default all other components of the environment are protected as well [1]. Indeed, humans are among the most sensitive organisms to radiation and
their protection does ensure protection of much of the environment. However, a more
satisfying approach for many stakeholders, and one that is in-line with protection strategies
implemented for other types of environmental contaminants, is to explicitly show that the
environment is protected. Therefore, the International Commission on Radiological Protection
(ICRP) now recommends explicit consideration of the environment and new approaches are
being developed to demonstrate such protection. Appropriately, the new developments strive to protect populations or higher organizational levels (e.g. communities, ecosystems [2]),
rather than focusing on the protection of individuals. The protection of higher levels of biological organization was not originally addressed [3], but is now being considered further
[4].
During the last 10 years, considerable progress has been made in deriving screening
ecological benchmarks and in developing a tiered Ecological Risk Assessment (ERA)
approach for radioecology [5–7]. While the ERA-type approach is a substantial advancement
in radioecology, a lack of sufficient data prevents current ERA analyses from fully accounting
for the realistic environmental conditions to which organisms are exposed. Data are
insufficient to predict effects from chronic, low doses; variable dose rate regimes; multicontaminant
scenarios or multi-generational exposures; ecosystem level effects; or the
influence of variable life-history traits [8]. Additionally, most measurements of effects are
assayed on individuals within a population. Extrapolation is required to estimate population
level effects from the individual-based measurements, or to account for the knowledge gaps
mentioned above. The extrapolation uses assessment factors (or safety factors) that add conservatism and substantially increase uncertainties in risk assessments. Large uncertainties do little to promote confidence with the stakeholders of radioecology. Improvements are therefore needed
Assessment of the aquifers in the West Canning Basin-Pardoo - application of isotopic and hydrogeochemical techniques
No full textMulti-proxy evidence for small historical tsunamis leaving little or no sedimentary record
No full textThere has been considerable progress in tsunami research in recent years, yet most work has been focussed on identifying and understanding the evidence of large events. This study aimed to identify the evidence of small historical tsunamis in Lyttelton Harbour, New Zealand. The study area has been inundated by multiple relatively small historical tsunamis that left atypical sedimentary evidence (no sand) or no sediment. Shallow trenches revealed discontinuous layers of small grey mud clasts at various depths across the study area, most likely transported from the nearby tidal flats. The origin of these mud clast layers was investigated using a multi-proxy approach comprising sedimentological, geochemical and diatom analyses complemented by dating from 137Cs activity profiles and historical data. Subtle variations consistent with inclusions of marine mud such as a decrease in organic content and magnetic susceptibility and increases in geochemical markers (e.g. Ca/kcps, K/kcps, K/Rb, Si/Rb and Sr/Rb) were found in the sediment profile. Variations in diatom assemblages suggesting a marine influence were also recorded at similar depths, aligning with layers of mud clasts. Using 137Cs activity profiles and historical data, these deposits were attributed to the 1960 Chile Valdivia and 1964 Alaska tsunamis, as well as a possible earlier event. Sedimentary evidence for the 2010 Chile Maule tsunami was not found at the study site, but geochemical analysis of surface samples revealed marked changes in Ca, Cl, Sr and Ti concentrations, indicative of a change from a terrestrial to marine influence. This was used to identify the landward extent of inundation by the 2010 event. Ultimately, this study shows that a broad multi-proxy analysis can distinguish even the subtle signatures of an inconspicuous deposit laid down by a small tsunami. © 2017, Elsevier B.V
Crystal chemistry of the orthorhombic Ln2TiO5 compounds with Ln=La, Pr, Nd, Sm, Gd, Tb and Dy.
No full textThe crystal structures of seven samples of orthorhombic (Pnma) Ln2TiO5 compounds with Ln=La, Pr, Nd, Sm, Gd, Tb and Dy were refined by Rietveld analysis of synchrotron X-ray powder diffraction (S-XRD) data. With increasing size of the lanthanide cation, the lattice parameters increase systematically: c by only ~1.5% whereas both a and b by ~6% from Dy2TiO5 to La2TiO5.
The mean Ti–O bond length only increases by ~1% with increasing radius of the Ln cation from Gd to La, primarily due to expansion of the pair of Ti–O3 bonds to opposite corners of the Ti–O5 square based pyramid polyhedra. For Dy2TiO5 and Tb2TiO5, a significant variation in Ti–O1 and Ti–O4 bond lengths results in an increased deformation of the Ti–O5 base.
The particular configuration consists of large rhombic shaped tunnels and smaller triangular tunnels along the b axis, which have implications for defect formation and migration caused by radiation damage or the ionic conductivity.
© 2017 Elsevier B.V
Environmental impact of tsunami inundation on the Sendai plain
No full textLarge areas of farmland in the Sendai Plain, Japan, were inundated by the 11 March 2011 Tohoku-oki tsunami and covered by a discontinuous 30–0.2 cm thick sediment layer consisting of sand and/or mud and generally thinning and fining inland. Two months after the tsunami, numerous rice paddy fields and depressions remained ponded with brackish or saline water. A series of field surveys in May, August and October 2011 were carried out north of Sendai airport, in order to assess the environmental impact of the tsunami. While evaporation had resulted in elevated conductivity in ponded water in May (up to 68.2 mS cm− 1), rainfall over the next five months led to dilution, although brackish water was still recorded in depressions and on paddy fields. Tsunami sediments, underlying soil and soil beyond the tsunami inundation limit were collected at 43 sites along and near a transect extending over 5 km inland, and analysed for grain size, organic content, water leachable ions, acid leachable metals and exchangeable metalloids. Water leachable anion and cation concentrations were elevated in sandy and muddy tsunami deposits and soils particularly in areas, where seawater had stagnated for a longer period of time after the tsunami, with up to 10.5% Cl, 6.6% Na, 2.8% SO4, 440 mg kg− 1 Br measured in surface sediments (< 0.5 cm depth). Vertical variations were also recorded, with higher concentrations often measured in the surface samples. A similar trend could be observed for some of the metalloids (As) and metals (Zn, Cu and Ni), although in general, maximum concentrations of metals and metalloids were not much higher than in soils not inundated by the tsunami and were within background levels for uncontaminated Japanese soils.
The impact of saltwater inundation was documented in the chemistry of soils underlying tsunami sediments, which were affected by salt contamination down to ~ 15 cm depth, and soils not covered by tsunami deposits. The latter implies that the extent of tsunami inundation may successfully be determined using geochemical markers in absence of any sedimentological evidence. Water leachable ions mostly decreased over time, however, they remained high enough to impact on rice farming, which was completely halted in 2011. Although further work is required to assess the longer term impact of tsunami inundation, flushing of salt with freshwater, as well as the possible removal of sandy/muddy sediments and underlying soil are recommended to allow crop production to resume