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Uranium(VI) hybrid materials with [(UO2)3(µ3‐O)(µ2‐OH)3]+ as the sub–building unit via uranyl–cation interactions
No full textThe hydrothermal reaction of uranyl nitrate with 1,4-benzenedicarboxylic acid (H2bdc) in the presence of strontium or potassium hydroxides and nitrates afford the formation of two new uranyl hybrid materials featuring extensive uranyl-strontium or uranyl-potassium interactions with [(UO2)3(µ3-O)(µ2-OH)3]+ as the sub-building unit. Sr1.5[(UO2)12(O)3(OH)13(bdc)4]⋅6H2O (1) contains one-dimensional (1D) uranyl oxohydroxyl ribbons made of trinuclear pentagonal bipyramidal uranyl units. The ribbons are linked together via uranyl-strontium interactions to form 2D inorganic domains which are further connected through µ4-bdc anions forming a 3D hybrid structure. This is the first reported uranyl-strontium interaction in extended hybrid solid with the shortest Sr-O−yl bond length of 2.596 (8) Å. K3[(UO2)12(O)3(OH)13(bdc)4]⋅8H2O (2) has a similar 3D hybrid structure built up through extensive K-O−yl interactions with the shortest K-O−yl bond length of 2.620 (6) Å. Raman spectroscopy has confirmed the presence of oxo-bridging (U−O−U) vibrations. Thermal stabilities and photoluminescent properties are reported. © 2016 WILEY‐VCH Verlag GmbH & Co
Spring root-zone temperature regulates root growth, nutrient uptake and shoot growth dynamics in grapevines
No full textAbstract
Background and Aims
Environmental factors such as root-zone temperature can influence plant development. Linkages between spring soil temperature, carbohydrate reserve mobilisation, nutrient uptake and nitrogen partitioning were investigated in Shiraz grapevines to gain better understanding of how this abiotic factor can alter root and canopy development.
Methods and Results
Plants were exposed to a cool, an ambient or a warm root-zone temperature over a 9-week period from budburst. Root starch mobilisation was correlated to the sum of cumulative heat units absorbed by the soil (soil growing degree days, GDDsoil) and this contributed to greater fine root density and extent of root branching. Most macronutrients, including N, accumulated to greater concentration in the leaves of vines exposed to the warm root-zones. Patterns of 15N accumulation indicated that despite greater fertiliser-N uptake in the warm root-zone treatment, most of the N that accumulated in the shoots was the result of N reserve mobilisation. Warmed root-zones resulted in plants with accelerated leaf emergence, extended internodes and elongated shoots with larger leaves. Plant leaf area and shoot dry mass were both positively correlated to GDDsoil, but inversely correlated to root starch concentration, indicating a link between root carbohydrate reserve mobilisation and shoot growth.
Conclusions
Warm soils stimulated root starch and N mobilisation, root growth and primary nutrient uptake with further consequences on canopy growth and altered N partitioning among the plant components.
Significance of the Study
Following winter dormancy, GDDsoil can thus be used to model above- and below-ground plant growth responses in the grapevine.© 2015 Australian Society of Viticulture and Oenology Inc
Identifying flood and drought events using a 500-year reconstruction of rainfall in the Australian subtropics as determined from hoop pine (Araucaria cunninghamii) tree rings
No full textSubtropical Australia is highly susceptible to extreme events like the catastrophic floods that occurred in Southeast Queensland (SEQ) in 2011. This event was suggested to be a 1 in 1000 year flood, however, preliminary research of past flood deposits has indicated that a similar sized event occurred about 200 years ago. Our understanding of the past frequency of these types of events is limited because there are few long-term climate records available for this region. Historical precipitation records extend back to the 19th century, which is not of a sufficient duration to understand extreme event frequencies. Other annual proxy methods of rainfall reconstruction are needed to better understand the flood and drought history of this area. Tree rings provide an annual record of past conditions based on a single environmental variable that is limiting tree growth. Here we present the first long-term (>150 years) Australian subtropical tree ring reconstruction of rainfall from Lamington National Park, a natural area of rainforest on the southern boundary of SEQ. Hoop Pine (Araucaria cunninghamii) trees were used as they are one of the longest lived tree species in subtropical Australia, they grow in response to precipitation conditions, and they put on a visible annual ring that can be measured. This record was developed using a multi-technique approach where traditional ring width measuring, X-ray densitrometry, and radiocarbon dating were combined to create a robust chronology that was then used to reconstruct rainfall. Years with major rainfall events are confirmed through Calcium and Strontium signals identified in the tree rings using ITRAX XRF trace elements. Climate conditions for years with known flood and drought events were then compared to our reconstruction to identify potential extreme events in SEQ beyond the period of instrumental record. The methodology, results, and future directions of this research will be discussed
Towards a universal “baseline” characterisation of air masses for high- and low-altitude observing stations using Radon-222
Get PDFWe demonstrate the ability of atmospheric radon concentrations to reliably and unambiguously identify local and
remote terrestrial influences on an air mass, and thereby the potential for alteration of trace gas composition by
anthropogenic and biogenic processes. Based on high accuracy (lower limit of detection 10–40 mBq m–3), high temporal
resolution (hourly) measurements of atmospheric radon concentration we describe, apply and evaluate a simple two-step
method for identifying and characterising constituent mole fractions in baseline air. The technique involves selecting a
radon-based threshold concentration to identify the “cleanest” (least terrestrially influenced) air masses, and then
performing an outlier removal step based on the distribution of constituent mole fractions in the identified clean air
masses. The efficacy of this baseline selection technique is tested at three contrasting WMO GAW stations: Cape Grim (a
coastal low-altitude site), Mauna Loa (a remote high-altitude island site), and Jungfraujoch (a continental high-altitude
site). At Cape Grim and Mauna Loa the two-step method is at least as effective as more complicated methods employed to
characterise baseline conditions, some involving up to nine steps. While it is demonstrated that Jungfraujoch air masses
rarely meet the baseline criteria of the more remote sites, a selection method based on a variable monthly radon threshold
is shown to produce credible “near baseline” characteristics. The seasonal peak-to-peak amplitude of recent monthly
baseline CO2 mole fraction deviations from the long-term trend at Cape Grim, Mauna Loa and Jungfraujoch are estimated
to be 1.1, 6.0 and 8.1 ppm, respectively
Structural and thermal transitions during the conversion from native to granular cold-water swelling maize starch
No full textNative maize starch was gradually converted into granular cold-water swelling starch (GCWSS) by aqueous ethanol treatments at elevated temperatures. At a treatment temperature of 95 °C, decreasing ethanol concentrations from 68 to 48% (v/v) led to decreased post-treatment gelatinization enthalpies in excess water, reflecting remaining original A-type crystals. Concomitantly to native A-type crystal melting, VH-type crystals appeared. At an ethanol concentration of 48%, a granular cold-water swelling maize starch was successfully produced. All crystals in its intact granules were of the VH-type and appeared birefringent when studied in ethanol under polarized light. Removal of all residual solvent by high temperature drying did not influence swelling power, proving that a high temperature drying step is not necessary to induce cold-water swelling capacity. Based on in situ calorimetric measurements, the thermal requirements to produce GCWSS from different ethanol:water mixtures were elucidated. This work is the first to demonstrate that the amylose fraction contributes almost exclusively to VH-type crystal formation in GCWSS. © 2014, Elsevier Ltd
SIRIUS - A new 6MV accelerator system for IBA and AMS at ANSTO
No full textThe Centre for Accelerator Science (CAS) facility at ANSTO has been expanded with a new 6 MV tandem accelerator system supplied by the National Electrostatic Corporation (NEC). The beamlines, end-stations and data acquisition software for the accelerator mass spectrometry (AMS) were custom built by NEC for rare isotope mass spectrometry, while the beamlines with end-stations for the ion beam analysis (IBA) are largely custom designed at ANSTO. An overview of the 6 MV system and its performance during testing and commissioning phase is given with emphasis on the IBA end-stations and their applications for materials modification and characterisation. © Elsevier B.V
Roles of forest bioproductivity, transpiration and fire in a nine-year record of cave dripwater chemistry from southwest Australia
No full textForest biomass has the potential to significantly impact the chemistry and volume of diffuse recharge to cave dripwater via the processes of nutrient uptake, transpiration and forest fire. Yet to-date, this role has been under-appreciated in the interpretation of speleothem trace element records from forested catchments. In this study, the impact of vegetation is examined and quantified in a long-term monitoring program from Golgotha Cave, SW Australia. The contribution of salts from rain and dry-deposition of aerosols and dissolved elements from soil mineral and bedrock dissolution to dripwater chemistry are also examined. This study is an essential pre-requisite for the future interpretation of trace element data from SW Australian stalagmite records, whose record of past environmental change will include alterations in these biogeochemical fluxes. Solute concentrations in dripwater vary spatially, supporting the existence of distinct flow paths governed by varying amounts of transpiration as well as nutrient uptake by deeply-rooted biomass. Applying principal components analysis, we identify a common pattern of variation in dripwater Cl, Mg, K, Ca, Sr and Si, interpreted as reflecting increasing transpiration, due to forest growth. Mass-balance calculations show that increasing elemental sequestration into biomass has the largest impact on SO4, providing an explanation for the overall falling dripwater SO4 concentrations through time, in contrast to the transpiration-driven rising trend dominating other ions. The long-term rise in transpiration and nutrient uptake driven by increased forest bioproductivity and its impact on our dripwater chemistry is attributed to (i) the post-fire recovery of the forest understorey after fire impacted the site in 2006 CE; (ii) and/or increased water and nutrient demand as trees in the overlying forest mature. The impact of climate-driven changes on the water balance is also examined. Finally, the implications for interpreting SW Australian speleothem trace element records are discussed. © 2016, Elsevier Ltd
Exploring the source-to-sink residence time of terrestrial pollen deposited offshore Westland, New Zealand.
No full textThe occurrence of terrestrial palynomorphs in Quaternary marine sedimentary sequences allows for direct land–sea correlations and provides a means for transferring Marine Isotope Stage chronologies to terrestrial records that extend beyond the range of radiocarbon dating. Both of these important applications require an implicit assumption that the lag between pollen release and final deposition on the seafloor – here referred to as source-to-sink residence time – is negligible in relation to the chronological resolution of the sedimentary sequence. Most studies implicitly assume zero lag, and where studies do take palynomorph residence time into account, its magnitude is rarely quantified. In Westland, New Zealand, fluvial transport is the main source of delivery of terrestrial pollen offshore to the adjacent East Tasman Sea. We radiocarbon-dated organic matter carried and deposited by contemporary Westland rivers that drain catchments with varying degrees of disturbance. The ages obtained ranged widely from essentially modern (i.e., − 57 ± 22 cal yr BP) to 3583 ± 188 cal yr BP, suggesting that precisely constraining the residence time in this region is unlikely to be achieved. We also compared the timing of four palynomorph events characterising Westland's late Pleistocene, along with the well-dated Kawakawa/Oruanui Tephra (KOT), between marine core MD06-2991 and four terrestrial records from Westland. Critically, all palynomorph events and the KOT are chronologically indistinguishable with respect to the independently dated marine and terrestrial records, supporting the general principle of transferring the marine chronology onto the terrestrial records in this setting. In other regions, particularly those lacking the high soil production and erosion rates that characterise Westland, we suggest that similar tests of marine residence time should be conducted before assumptions of zero or negligible lag are invoked.© 2016, Elsevier B.V
Key role of Bismuth in the magnetoelastic transitions of Ba3BiIr2O9
No full textThe key role played by bismuth in an average intermediate oxidation state in the magnetoelastic spin-gap compounds Ba3BiRu2O9 and Ba3BiIr2O9 has been confirmed by systematically replacing bismuth with La3+ and
Ce4+. Through a combination of powder diffraction (neutron and synchrotron),
X-ray absorption spectroscopy, and magnetic properties measurements, we show
that Ru/Ir cations in Ba3BiRu2O9 and Ba3BiIr2O9 have oxidation states between
+4 and +4.5, suggesting that Bi cations exist in an unusual average oxidation state
intermediate between the conventional +3 and +5 states (which is confirmed by
the Bi L3-edge spectrum of Ba3BiRu2O9). Precise measurements of lattice
parameters from synchrotron diffraction are consistent with the presence of
intermediate oxidation state bismuth cations throughout the doping ranges. We
find that relatively small amounts of doping (∼10 at%) on the bismuth site
suppress and then completely eliminate the sharp structural and magnetic
transitions observed in pure Ba3BiRu2O9 and Ba3BiIr2O9, strongly suggesting that the unstable electronic state of bismuth plays a
critical role in the behavior of these materials. © 2013, American Chemical Society
The role of neutron scattering in magnetic storage materials research
No full textAs the demand for highly functional magnetic storage materials grows, the need to understand the basic physical properties behind these materials has become key to engineering storage devices. Neutron scattering techniques provide a way to probe the magnetic properties of potential memory materials. The highlighted techniques, polarized neutron reflectometry, small angle neutron scattering, and neutron diffraction, are sensitive to not only nuclear but also magnetic structure and are capable of investigating a large range of real space length scales. In this paper, we review recent research on magnetic thin films and layered systems with potential for storage applications. We focus on several important aspects of layered magnetic memory devices, including exchange bias, interfaces and interactions between layers, and magnetic reversal. © 2014, IEEE