4051 research outputs found
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Chemical delithiation and exfoliation of LixCoO2
No full textProgressive chemical delithiation of commercially available lithium cobalt oxide (LiCoO2LiCoO2) showed consecutive changes in the crystal properties. Rietveld refinement of high resolution X-ray and neutron diffraction revealed an increased lattice parameter c and a reduced lattice parameter a for chemically delithiated samples. Using electron microscopy we have also followed the changes in the texture of the samples towards what we have found is a critical layer stoichiometry of about LixCoO2LixCoO2 with x=1/3 that causes the grains to exfoliate. The pattern of etches by delithiation suggests that unrelieved strain fields may produce chemical activity
Impoundment constraint of fish niche diversity in a temperate Australian river.
No full textDams constitute a major threat to aquatic ecosystems world-wide by modifying habitat and impairing opportunities for many freshwater fish. Subsequently, there can be a loss in fish diversity and change in the species distributions and population structure that ultimately contribute to changes in trophic structure and ecosystem function. In this study, stable isotope analysis (SIA) was used to compare trophic interaction and niche space of five fish species residing upstream and downstream of a significant barrier (Tallowa Dam) on the Shoalhaven River in south-eastern Australia. Significant reduction in niche space was found among predator/prey species residing in upstream habitat, implying limited dietary opportunity. Mixing calculations for Macquaria novemaculeata confirmed ontogenetic differences upstream and downstream of the dam. Causal mechanisms for this variability in trophic structure include habitat modification and/or discontinuity in river connectivity. SIA provides a useful tool for demonstrating the effect of barriers and/or impoundments on aquatic ecosystems, and for developing future monitoring programmes to evaluate restoration strategies
The efficiency of charcoal decontamination for radiocarbon dating by three pre-treatments – ABOX, ABA and hypy
No full textHere we report results of a direct inter-comparison of the ability of three radiocarbon pre-treatment techniques to remove radiocarbon contamination introduced by exposing known-radiocarbon-free charcoal made at three different temperatures (300, 400 and 500 °C) to environmental contamination on a rainforest floor for one to three years. The initial charcoal had no measureable radiocarbon, but 14C activity increased after environmental exposure to ∼1 pMC after one year (apparent age of ∼40,000 yrs BP) and ∼5 pMC after three years (apparent age of ∼25,000 years). For the 400 and 500 °C samples, all techniques were able to reduce contamination by >90%. Acid–base oxidation (ABOX) provided the most reliable decontamination, reducing the radiocarbon activity of the one year samples to background, and reducing the radiocarbon activity of the three year samples to 0.04 ± 0.02 pMC or less (apparent age >56,900 yrs BP). The performance of ABOX was superior to that of both acid–base–acid (ABA) and hydrogen pyrolysis (hypy) treatments, with ABA performing better than hypy in most cases. No technique was able to fully remove decontamination from the 300 °C charcoal (although ABOX again removed the most contamination), likely due to the incompletely pyrolized nature of the charcoal which is dominated by aromatic clusters of small ring size. All the techniques rely on removing contaminant carbon faster than indigenous carbon and this condition is not met in the case of charcoal produced at temperatures below ∼350 °C. While all pre-treatments are useful for routine sample processing, the results suggest that ABOX is the only technique that can provide reliable decontamination of charcoal of an age close to the dating limit of the radiocarbon dating technique.© 2014, Elsevier B.V
Deuterium retention and near-surface modification of ion-irradiated diamond exposed to fusion-relevant plasma
No full textChemical vapour deposited diamond was irradiated with 5 MeV carbon ions to simulate the damage caused by collision cascades from neutron irradiation in a fusion environment. Ion-irradiated samples were then exposed to a deuterium plasma in MAGPIE with ion flux of ~1.3 × 1021 ions m−2 s−1. Raman and near edge x-ray absorption fine structure (NEXAFS) spectroscopy were used to characterize the degree of disorder and sp2-bonding induced by the ion irradiation. The signals of sp2-bonded and disordered carbon were observed to decrease after exposure to the deuterium plasma, although sharp Raman peaks indicative of vacancy and interstitial defects induced by the MeV ions were less affected. Recovery of a diamond-like surface after plasma exposure was evident in the NEXAFS spectra. Elastic recoil detection analysis showed that the ion-damaged diamond retained more deuterium than diamond exposed only to deuterium plasma. For the case of unirradiated samples, diamond retained more deuterium than graphite. However, for the case of the ion-irradiated samples, diamond exhibited less deuterium retention than graphite. © 2014, IAEA Vienna
Phenylene bolaamphiphiles: Influence of the substitution pattern on the aggregation behavior and the miscibility with classical phospholipids
No full textThe synthesis of two symmetric single-chain phenylene-modified bolaamphiphiles with meta and ortho phenyl substitution pattern is described. The aggregation behavior of both bolaamphiphiles in aqueous suspension was investigated by differential scanning calorimetry (DSC), transmission electron microscopy (TEM), Fourier-transform IR (FTIR) spectroscopy, and small angle neutron scattering (SANS). We could show that a change in the substitution pattern from para to meta or ortho leads to a change in the aggregation behavior so that small micelles instead of nanofibers are formed. Furthermore, the mixing behavior of these bolaamphiphiles with classical bilayer forming phospholipids, such as 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) was studied by means of DSC, TEM, cryo-TEM, and small angle X-ray scattering (SAXS). The aim was to stabilize bilayer membranes formed by classical phospholipids by incorporation of bolaamphiphiles to obtain liposomes with improved stability suitable for drug delivery purposes. We could show that the phenylene-modified bolaamphiphiles are indeed miscible with DPPC and DSPC; however, closed vesicles as observed for pure DPPC and DSPC were not found. Instead, small disk-like aggregates are formed. In the case of mixtures of phenylene-modified bolaamphiphiles with DPPC, these bilayer disks have a higher DSC transition temperature compared to pure DPPC indicating an increased stability of the ordered gel phase inside the disks.© 2014 WILEY-VCH Verlag
Topotactic structural conversion and hydration-dependent thermal expansion in robust LnMIII(CN)6·nH2O and flexible ALnFeII(CN)6·nH2O frameworks (A = Li, Na, K; Ln = La–Lu, Y; M = Co, Fe; 0 ≤ n ≤ 5)
No full textThe structures of the AxLnM(CN)6·nH2O (A = Li, Na, K; Ln = La–Lu, Y; M = Co, Fe; x = 0, 1; 0 ≤ n ≤ 5) cyanide frameworks, their thermal expansion behaviour, and their transformations upon dehydration are explored using X-ray and neutron single crystal diffraction and X-ray powder diffraction. Modification from positive to negative thermal expansion in the LnCo(CN)6·nH2O phases is achieved by removal of the guest water molecules. Most notable is the unprecedented flexibility demonstrated by the “coiling” of KLnFe(CN)6·nH2O frameworks upon their dehydration, wherein the lanthanoid coordination geometry reversibly converts from a 9-coordinate tri-capped trigonal prism to a 6-coordinate octahedron via a single-crystal-to-single-crystal process, accompanied by a large (14–16%) decrease in unit cell volume. © 2014, The Royal Society of Chemistry
Terrestrial LiDAR survey and morphological analysis to identify infiltration properties in the Tamala Limestone, Western Australia.
No full textCaves are an ideal observatory of infiltration water in karstified limestone, and the application of remote sensing techniques can bring new insights toward flow patterns and processes. We present an exhaustive characterization of Golgotha Cave in SW Western Australia, based on a light detection and ranging (LiDAR) measurement campaign. The cave is developed in Quaternary age aeolianite (dune limestone) and its infiltration waters form speleothems. We collect ground-based LiDAR scans of the cave ceiling at three sites within the cave system. The resulting point-clouds are analyzed using mathematical morphology to determine statistical information on stalactite widths, lengths, and spatial distributions. We establish a relationship between stalactite diameter and length that is in agreement with the platonic ideal of stalactite shape. We relate stalactite density variation with topography of the cave ceiling and variations in hydraulic gradient. From this analysis, it appears that longer stalactites tend to occur in comparatively lower ceiling elevation, which, we hypothesize, represents greater mass of water in the limestone above the roof of the cave. We also investigate the relationship between stalactite distribution and ceiling features such as fractures. We apply this to identify different types of possible flow patterns such as matrix flow and fracture flow. This analysis demonstrates a spatial variability, with one site having linear groups of stalactites and another site mostly dominated by stalactite clusters. © 2015, IEEE
Improving estimates of pollution outflow at Gosan using 222Rn’
No full textThe best understanding of climatic, ecological
and health effects from increasing
Southeast Asian emissions will likely be achieved
by models coupled to detailed emission
inventories and remote sensing data. To improve
model accuracy and forecast horizons,
careful evaluation against appropriate observations
is essential. To minimize the
chance of misleading comparisons, it is important
to ensure ground-based reference observations
are well matched with the model
output, especially regarding fetch regions and
scales of observation. To quantify upstream
emissions based on ground-based observations
it is necessary to: (i) understand the measurement
“footprint”, (ii) identify observations
most representative of air that has been in
good contact with the surface over which it
has travelled, and has not been significantly
diluted by fronts or deep convection in transit,
(iii) ensure observations are representative
of the whole boundary layer (BL), (iv) minimize
the influence of local emissions, (v)
characterize changes in mixing depth, and
(vi) characterize evolving “background”
concentrations
Surface exposure chronology of the Waimakariri glacial sequence in the Southern Alps of New Zealand: Implications for MIS-2 ice extent and LGM glacial mass balance
No full textDuring the late Quaternary, the Southern Alps of New Zealand experienced multiple episodes of glaciation with large piedmont glaciers reaching the coastal plains in the west and expanding into the eastern alpine forelands. Here, we present a new 10Be exposure age chronology for a moraine sequence in the Waimakariri Valley (N-Canterbury), which has long been used as a reference record for correlating glacial events across New Zealand and the wider Southern Hemisphere. Our data indicate that the Waimakariri glacier reached its maximum last glaciation extent prior to ∼26 ka well before the global last glaciation maximum (LGM). This was followed by a gradual reduction in ice volume and the abandonment of the innermost LGM moraines at about 17.5 ka. Significantly, we find that during its maximum extent, the Waimakariri glacier overflowed the Avoca Plateau, previously believed to represent a mid-Pleistocene glacial surface (i.e. MIS 8). At the same time, the glacier extended to a position downstream of the Waimakariri Gorge, some 15 km beyond the previously mapped LGM ice limit. We use a simple steady-state mass balance model to test the sensitivity of past glacial accumulation to various climatic parameters, and to evaluate possible climate scenarios capable of generating the ice volume required to reach the full local-LGM extent. Model outcomes indicate that under New Zealand's oceanic setting, a cooling of 5 °C, assuming modern precipitation levels, or a cooling of 6.5 °C, assuming a one third reduction in precipitation, would suffice to drive the Waimakariri glacier to the eastern alpine forelands (Canterbury Plains). Our findings demonstrate that the scale of LGM glaciation in the Waimakariri Valley and adjacent major catchments, both in terms of ice volume and downvalley ice extent, has been significantly underestimated. Our observation that high-lying glacial surfaces, so far believed to represent much older glacial episodes, were glaciated during the LGM, challenges the conventional geomorphic model of glaciation in New Zealand where the vertical arrangement of glacial landform-associations is used to assign successively older glaciation ages. © 2015, Elsevier B.V
Isotopic and hydrogeochemical study of radionuclide and landfill leachate migration in a contaminant disposal precinct in Sydney´s Southwest.
No full textDuring the 1960s the Australian Atomic Energy Commission disposed of low level radioactive waste
in shallow trenches at the Little Forest Legacy Site (LFLS). Radionuclides included small amounts of
plutonium, uranium, fission products Cs-137 and Sr-90, and tritium. Adjacent sites were used for
disposal of night soil, municipal waste and industrial liquid waste. Contaminant distributions,
groundwater levels, environmental isotopes and hydrogeochemistry were measured at LFLS to assess the relative importance of different contaminant transport pathways, sources and mechanisms and support management of the site. Sources include the LFLS waste, fallout from
nuclear weapons testing, and adjacent landfills which contain some artificial radioactive substances.
Tritium is a conservative tracer of subsurface water movement, and has been used to identify
potential contaminant pathways at the LFLS. In addition, variations in Sr-87/Sr-86, δC-13(DIC) and
evolution of δS-34 have been used to help identify processes occurring at the site. Within the
trenches, the degradation of organic matter results in localised methanogenesis, as suggested by
enriched δH-2 and δC-13(DIC) values in adjacent subsurface water. The isotopic signatures enable
differentiation of LFLS contaminants from those originating from nearby sources including an
adjacent quarry used for municipal waste which contributes leachate (characterised by elevated
tritium, enriched δH-2 and δC-13(DIC) as well as a chemical signature) into the underlying
groundwater system. The study has shown “bathtubbing” (overflow of waste trenches during
rainfall events) to be an important mobilisation mechanism, contributing to tritium movement at
the site and localised migration of radionuclides (particularly actinides Pu and Am) from trenches to
surface soils. However sub-surface migration of actinides from the LFLS trenches has been retarded
by low transmissivity clay-rich soils. The value of hydrogeochemical and isotopic tracers in
understanding hydrological and contaminant transport processes is demonstrated by this work and will contribute to future management of the precinct