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Small-angle scattering as a tool to study the thermal denaturation of DNA
No full textDNA thermal denaturation is the breaking of the base pairs, leading to a splitting of the two strands of the double helix. While it is easy to measure the fraction of open base pairs vs. temperature, determining the fraction of fully open molecules is much harder. Previously, the simultaneous recording of f and p could only be achieved for special sequences. We show that small-angle scattering of X-rays or neutrons allows the measurement of p for any sequence. We illustrate the method with a SAXS investigation of two sequences designed to exhibit different melting profiles and compare the SAXS data with nano-calorimetric measurements of the melting curve. © 2014, EPLA
A Holocene record of climate and hydrological changes from Little Llangothlin Lagoon, south eastern Australia
No full textWe present a new well dated Holocene record of environmental change from Little Llangothlin Lagoon in eastern Australia derived from aquatic plant macrofossils, macroscopic charcoal flux, and sediment stratigraphy from multiple cores. Little Llangothlin was an ephemeral freshwater wetland exhibiting frequent dry phases between 9800 and 9300 calendar years before present (cal. yr BP). There was a switch to a more positive water balance after 9300 cal. yr BP, and by 8000 cal. yr BP, there was a lake that persisted until 6100 cal. yr BP. The period between 6100 and 1000 cal. yr BP was much drier, and there is no evidence for a permanent lake during this period. The Little Llangothlin record provides evidence for a wet phase during the Early to Middle Holocene (9000–6000 cal. yr BP) from the boundary region between temperate and tropical influences in eastern Australia. We propose that generally enhanced circulation after 9000 cal. yr BP explains the pattern of increasing moisture at the site at this time. The later Holocene climate at the site is consistent with other sites in south east Australia with a switch to generally drier conditions after 6000 cal. yr BP
Synthesis, structure and conductivity of BaIn0.8Mn0.2O3 − δ
No full textGreen BaIn0.80Mn0.20O2.70 (S1) has been synthesized by solid-state reaction under high temperature, and black BaIn0.80Mn0.20O2.60 (RS1) is obtained by treating S1 under vacuum at 500 °C. They were characterized by powder X-ray and neutron diffraction, selected area electron diffraction, magnetic measurement, and impedance spectrum. S1 and RS1 crystallize in Cmcm (a = 5.9722(3), b = 5.9664(3), c = 8.4511(4) Å) and P21/c (a = 5.9328(7), b = 5.9445(11), c = 16.8154(14) Å, β = 90.02(2)°), respectively. Oxide ion vacancies are confirmed to exist in S1 and RS1 by the neutron diffraction data. © 2014, Elsevier B.V
High rate capability core–shell lithium titanate@ceria nanosphere anode material synthesized by one-pot co-precipitation for lithium-ion batteries
No full textCore–shell Li4Ti5O12@CeO2 nanosphere has been synthesized by a one-pot co-precipitation method. The structure and morphology of the as-prepared materials have been analyzed by X-ray diffraction and transmission electron microscopy. The results show that CeO2 is successfully coated on the surface of the Li4Ti5O12 besides partial doping of Ce4+ into the Li4Ti5O12 structure. The Li4Ti5O12@CeO2 nanosphere exhibits excellent capacity of 152 mAh g−1 even after 180 cycles at 10 C, with no noticeable capacity fading. Furthermore, the sample shows much improved rate capability at 40 C compared with pure Li4Ti5O12 when used as anode material for lithium-ion batteries. The introduction of CeO2 enhances not only the electric conductivity of Li4Ti5O12, but also the lithium ion diffusivity in Li4Ti5O12, resulting in significantly improved electrochemical performance of the Li4Ti5O12. © 2014, Elsevier B.V
Lineshape of the singlet-triplet excitations in the dimer system Sr 3 Cr 2 O 8 to first order in the high-density 1/z expansion
No full textThe Cr 5+ ions in Sr 3 Cr 2 O 8 constitute a strongly correlated spin-1/2 dimer system. Experiments show that the collective singlet-triplet excitations in this system are well defined in the zero-temperature limit, but, when heated, the inelastic neutron scattering peaks decrease rapidly in intensity and acquire a nonzero line width. When including the fluctuations to leading order in 1/z , where z is the coordination number, the diagrammatic high-density expansion is found to offer an accurate description of the singlet-triplet excitations. The theory explains not only the temperature dependencies of the intensities and line widths, but also that strong correlation causes the lineshapes to become asymmetric at temperatures comparable to the excitation energies.© 2014, American Physical Society
New synthesis route for lead zirconate titanate powder
No full textPhase pure lead zirconate titanate (PZT) powder was produced via a new aqueous coprecipitation method. A suite of characterization techniques, including FTIR, Raman, X-ray diffraction, SEM as well as nitrogen sorption were employed to investigate the structural evolution of the synthesized and calcined powder. The dried precipitate formed in aqueous phase yielded approximately 80 wt% final product after calcination. The PZT perovskite structure was obtained after calcination at 550 °C for 3 h. Milling of the calcined powder reduced the mean particle size from approximately 10 µm to 2 µm. With increasing calcination temperature from 550 °C to 700 °C, both surface area and pore volume decreased while pore size increased from 3.4 nm to 9.8 nm. The bulk density of pelletized samples increased from 4.83 to 7.57 g/cm3 with increasing sintering temperature from 800 °C to 1200 °C. Powder processing using this aqueous route is simple and reproducible leading to a method that is readily scalable for industrial applications. © 2016 Elsevier Ltd
Extended residence times for foraminifera in a marine-influenced terrestrial archaeological deposit and implications for palaeoenvironmental reconstruction.
No full textAccelerator Mass Spectrometry (AMS) radiocarbon dating and taphonomic grading was undertaken on foraminifera preserved in the archaeological shell matrix site of Thundiy, Bentinck Island, southern Gulf of Carpentaria, Australia. Foraminifera were assigned to one of six taphonomic grades ranging from pristine to severely abraded. AMS dating demonstrates a weak relationship between preservation status and age. Foraminifera ages are inconsistent with multiple ages on marine shell from the same deposit implying significant sediment transport system residence ages (the time between death of the organism and final deposition) for foraminifera in the deposit. Results demonstrate that foraminifera cannot be assumed to be contemporary with other components of the sedimentary context in which they occur, indicating that caution is required in interpreting chronologies and palaeoenvironmental records based on foraminifera recovered from highly dynamic depositional settings. Findings point to the potential of foraminifera AMS dating of coastal archaeological deposits to contribute to evaluations of site integrity and chrono-stratigraphic analyses. © 2015, Elsevier Ltd
Late Quaternary changes in the westerly winds over the Southern Ocean – a progress report
No full textThe Southern Hemisphere westerly winds (SHW) are the strongest time-averaged oceanic winds. They drive the circulation of the Southern Ocean and changes in their strength and position are thought to modify
the upwelling of carbon rich deep water, exerting significant control on the ocean-atmosphere balance of
CO2. Thus changes in the SHW, such as the recently observed intensification, could influence whether
the Southern Ocean acts as a net source or sink of atmospheric CO2, with major implications for global
climate. At present the relationships between wind strength, CO2 and climate are poorly understood and
there are very few studies within the core belt of the SHW in the sub-Antarctic zone c.46 to 60 deg South.
We have been attempting to address this by producing centennial to decadal reconstructions of changes in
SHW strength at sub-Antarctic islands in each of the major sectors of the Southern Ocean. In this talk we
will show how lake sediments and peat deposits on the west coasts of these islands can yield proxy-based reconstructions of past changes in the SHW. We will review the statistical performance of our inference
models, their application down selected sediment cores, and compare them with complimentary proxies of
changes in wind strength based on precipitation and minerogenic inputs. The next phase of the project will
use GCM simulations to help understand the patterns seen in the observational data and identify the drivers of past changes in the SHW
Estimates of late Holocene soil production and erosion in the Snowy Mountains, Australia.
No full textSoil production in actively uplifting or high precipitation alpine landscapes is potentially rapid. However, these same landscapes are also susceptible to erosion and can be sensitive to changes in climate and anthropogenic activity which can upset the balance between soil production and erosion. The Snowy Mountains, southeastern Australia, are a tectonically stable, low relief, moderate precipitation mountain environment. The alpine area is extensively blanketed by soil that has been subjected to more intensive episodes of erosion during past periods of anthropogenic disturbance and under cold climate conditions of the late Quaternary. In this study, rates of soil development and hillslope erosion were investigated using radiocarbon dating, fallout radionuclides and sediment cores collected from lakes and reservoirs. Estimated Holocene soil development rates were 20–220 t/km2/y. Erosion rates determined from the radionuclides 137Cs and 210Pb were equivocal, due to the inherent spatial variability of radionuclide inventories relative to apparent erosion rates. Estimated average erosion rates over the past 100 years, determined from 210Pbex inventories, were 60 t/km2/y (95% CI: 10, 90). Inventories of 137Cs observed at the same site implied that more recent erosion rates (over the past 60 years) was below the detection limits of the sampling method applied here (i.e. < 70 t/km2/y). The upper estimate of 90 t/km2/y is comparable to the mean erosion rate estimated using the radionuclide method for uncultivated sites in Australia and is significantly lower than that measured at sites were vegetation cover was disturbed by livestock grazing prior to its exclusion from the alpine area in the 1940s CE. Low erosion and high soil production rates relative to the lowland soils are likely related to extensive vegetation cover, which, in this context, protects soils against erosion and contributes to the formation of organic alpine soils, that rapidly accumulate organic matter by comparison to other soil types.© 2016, Elsevier B.V
Element-specific depth profile of magnetism and stoichiometry at the La0.67Sr0.33MnO3/BiFeO3 interface
No full textDepth-sensitive magnetic, structural, and chemical characterization is important in the understanding and optimization of physical phenomena emerging at the interfaces of transition metal oxide heterostructures. In a simultaneous approach we have used polarized neutron and resonant x-ray reflectometry to determine the magnetic profile across atomically sharp interfaces of ferromagnetic La0.67Sr0.33MnO3/multiferroic BiFeO3 bilayers with subnanometer resolution. In particular, the x-ray resonant magnetic reflectivity measurements at the Fe and Mn resonance edges allowed us to determine the element-specific depth profile of the ferromagnetic moments in both the La0.67Sr0.33MnO3 and BiFeO3 layers. Our measurements indicate a magnetically diluted interface layer within the La0.67Sr0.33MnO3 layer, in contrast to previous observations on inversely deposited layers [P. Yu et al., Phys. Rev. Lett. 105, 027201 (2010)]. Additional resonant x-ray reflection measurements indicate a region of altered Mn and O content at the interface, with a thickness matching that of the magnetic diluted layer, as the origin of the reduction of the magnetic moment.© 2014, American Physical Society