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Raman, FTIR and XRD study of Icelandic tephra minerals: implications for mars
No full textEssential to the success of proposed planetary Raman spectroscopy missions will be the preparation of comprehensive libraries of spectra and a greater understanding of the current limitations of Raman spectroscopy. Seven samples of Icelandic tephra were analysed using X-ray diffraction (XRD), Raman spectroscopy and Fourier transform infrared (FTIR) as an analogue for Martian rocks. The results from these three spectroscopic techniques were compared with the success of mineral identification of each method differing. Some minerals such as ilmenite and flouroapatite were identified using XRD and not found in the Raman spectra. Olivine, hematite and anatase were detected by Raman spectroscopy but were not observed in the XRD patterns. The FTIR results gave essential information on the presence of H2O in the samples. The impact of fluorescence on Raman spectra of some minerals is still a major concern as this is the most likely reason for some of the diagnostic mineral peaks not showing in the Raman spectra. © 2015, John Wiley & Sons, Ltd
Assessment of a fast generated analytical matrix for rotating slat collimation iterative reconstruction: a possible method to optimize the collimation profile
No full textA polystyrene film spun onto polished silicon substrates was implanted with argon ions using plasma immersion ion implantation (PIII) to activate its surface for single-step immobilization of biological molecules. The film was subsequently investigated by X-ray and neutron reflectometry, ultraviolet (UV)–visible (vis) and Fourier transform infrared (FTIR) ellipsometry, FTIR and Raman spectroscopy, as well as nuclear reaction analysis to determine the structural and compositional transformations associated with the surface activation. The ion irradiation resulted in a significant densification of the carbon structure, which was accompanied by hydrogen loss. The density and hydrogen profiles in the modified surface layers were found to agree with the expected depths of ion implantation as calculated by the Stopping and Range of Ions in Matter (SRIM) software. The data demonstrate that the reduction in film thickness is due to ion-induced densification rather than the removal of material by etching. Characterization by FTIR, atomic force microscopy (AFM), ellipsometry, and X-ray reflectometry shows that polystyrene films modified in this way immobilize dense layers of protein (tropoelastin) directly from solution. A substantial fraction of the immobilized protein layer remains after rigorous washing with sodium dodecyl sulfate solution, indicating that its immobilization is by covalent bonding
Organ dose-rate calculations for small mammals at Maralinga, the Nevada test site, Hanford and Fukushima: A comparison of ellipsoidal and voxelized dosimetric methodologies
No full textRadiological dosimetry for nonhuman biota typically relies on calculations that utilize the Monte Carlo simulations of simple, ellipsoidal geometries with internal radioactivity distributed homogeneously throughout. In this manner it is quick and easy to estimate whole-body dose rates to biota. Voxel models are detailed anatomical phantoms that were first used for calculating radiation dose to humans, which are now being extended to nonhuman biota dose calculations. However, if simple ellipsoidal models provide conservative dose-rate estimates, then the additional labor involved in creating voxel models may be unnecessary for most scenarios. Here we show that the ellipsoidal method provides conservative estimates of organ dose rates to small mammals. Organ dose rates were calculated for environmental source terms from Maralinga, the Nevada Test Site, Hanford and Fukushima using both the ellipsoidal and voxel techniques, and in all cases the ellipsoidal method yielded more conservative dose rates by factors of 1.2–1.4 for photons and 5.3 for beta particles. Dose rates for alpha-emitting radionuclides are identical for each method as full energy absorption in source tissue is assumed. The voxel procedure includes contributions to dose from organ-to-organ irradiation (shown here to comprise 2–50% of total dose from photons and 0–93% of total dose from beta particles) that is not specifically quantified in the ellipsoidal approach. Overall, the voxel models provide robust dosimetry for the nonhuman mammals considered in this study, and though the level of detail is likely extraneous to demonstrating regulatory compliance today, voxel models may nevertheless be advantageous in resolving ongoing questions regarding the effects of ionizing radiation on wildlife
Strain-induced magnetic phase transition in SrCoO3−δ thin films
No full textIt has been well established that both in bulk at ambient pressure and for films under modest strains, cubic SrCoO3−δ (δ<0.2) is a ferromagnetic metal. Recent theoretical work, however, indicates that a magnetic phase transition to an antiferromagnetic structure could occur under large strain accompanied by a metal-insulator transition. We have observed a strain-induced ferromagnetic-to-antiferromagnetic phase transition in SrCoO3−δ films grown on DyScO3 substrates, which provide a large tensile epitaxial strain, as compared to ferromagnetic films under lower tensile strain on SrTiO3 substrates. Magnetometry results demonstrate the existence of antiferromagnetic spin correlations and neutron diffraction experiments provide a direct evidence for a G-type antiferromagnetic structure with Neél temperatures between TN∼135±10K and ∼325±10K, depending on the oxygen content of the samples. Therefore, our data experimentally confirm the predicted strain-induced magnetic phase transition to an antiferromagnetic state for SrCoO3−δ thin films under large epitaxial strain. © 2015 American Physical Society
On the use of radon for quantifying the effects of atmospheric stability on urban emissions
Get PDFRadon is increasingly being used as a tool for quantifying stability influences on urban pollutant concentrations. Bulk radon gradients are ideal for this purpose, since the vertical differencing substantially removes contributions from processes on timescales greater than diurnal and (assuming a constant radon source) gradients are directly related to the intensity of nocturnal mixing. More commonly, however, radon measurements are available only at a single height. In this study we argue that single-height radon observations should not be used quantitatively as an indicator of atmospheric stability without prior conditioning of the time series to remove contributions from larger-scale "non-local" processes. We outline a simple technique to obtain an approximation of the diurnal radon gradient signal from a single-height measurement time series, and use it to derive a four category classification scheme for atmospheric stability on a "whole night" basis. A selection of climatological and pollution observations in the Sydney region are then subdivided according to the radon-based scheme on an annual and seasonal basis. We compare the radon-based scheme against a commonly used Pasquill–Gifford (P–G) type stability classification and reveal that the most stable category in the P–G scheme is less selective of the strongly stable nights than the radon-based scheme; this lead to significant underestimation of pollutant concentrations on the most stable nights by the P–G scheme. Lastly, we applied the radon-based classification scheme to mixing height estimates calculated from the diurnal radon accumulation time series, which provided insight to the range of nocturnal mixing depths expected at the site for each of the stability classes. © 2015, Author(s)
Comparing the stability and chemistry of soil organic carbon protected via pyrogenesis, aggregation and mineral-association
No full textWe investigated the influence of soil texture and mineralogy on soil organic carbon (SOC) stability in two native soils of different texture and mineralogy from the Southern Highlands of NSW, Australia. To do this, a heavy-textured (clayey) soil and coarse-textured (sandy) soil were sampled at various depths to bedrock. The bulk samples were then fractionated into different particle-sizes and SOC content and stability measured using elemental analysis and radiocarbon analysis. Diffuse-reflectance infrared Fourier Transform spectroscopy was applied to infer molecular chemistry and variability in the soils, and investigate to SOC chemical structures associated with shifts in radiocarbon content of the soils. In both soils, the highest SOC content was found in the finest fraction, indicating that particle-size is a dominant control on SOC retention, independent of soil texture. In contrast, the mechanisms of SOC stabilization varied between the two soils, which we attribute to the differences in mineralogy and texture. In the coarse-textured soil, the chemical recalcitrance of charcoal was found to be the dominant stabilization mechanism in most of the soil profile, and the chemical recalcitrance of other aromatic structures may have contributed to SOC stability in subsoils. In the clayey soil, the most important stabilization mechanism throughout the soil profile was aggregation, which was centuries older than the mineral-associated organic matter in the soil. SOC was highly correlated with radiocarbon content and depth in both soils, so that SOC turnover may be limited by substrate availability at depths near bedrock in the soils. Comparing the radiocarbon ages of the two soils, the most stable carbon was (1) C stored in charcoal, followed by (2) C occluded within aggregates consisting of highly-charged clay minerals, (3) C associated with highly-charged clay minerals and Fe/Mn oxides, and (4) C associated with lowly-charged silicates or sandy aggregates. Our results indicate that there is a disconnect between SOC storage and SOC stability. Our findings have implications for SOC sequestration schemes, namely that trade-offs exist between enhancing SOC storage and enhancing SOC stability, and that texture and mineralogy should be considered when tailoring these schemes within an ecosystem
Numerical modelling and computer simulations
No full textThe development of armour materials and systems is a very expensive business, especially when it involves lengthy ballistic trials. Penetration and perforation events are also highly complex and involve competition between alternative failure mechanisms. The physical conditions within an impact zone also vary, with location, in temperature, strain-rate, strain, stress state and pressure. Numerical modelling and computer simulations help understand these complexities and add value to the design process. This chapter describes some of the underpinning principles by covering the range of computer codes available, the types of processors used, and the breadth of both yield strength models and damage criteria which are employed to describe how an armour material flows, fractures and fails. At the end of the chapter, four worked examples illustrate the choices available when modelling armour/anti-armour interactions. The annexures provide excellent sources of data for the various material models and failure criteria. © 2017, Elsevier
A natural laboratory for offshore paleotsunami studies: the Augusta Bay (Eastern Sicily-Italy)
No full textThe recent results obtained from a 6.7 m-long piston-core (MS06), collected 2.3 km offshore Augusta at a water depth of 72 m and made of an almost homogeneous dark gray mud dated back to the last 4500 yrs, stimulated our curiosity in searching for other similar signatures. In fact, quantitative micropaleontological analysis of benthic foraminifera assemblages highlighted 12 anomalous intervals, marked by peaks with high percentages of displaced epiphytic specimens and an increase in the sandy component. These anomalies were generally accompanied by a significant amount of Posidonia remnants, a localized concentration of molluscs and organic-rich bands. Thus, the twelve anomalous peaks were interpreted as the primary effect of tsunami waves (back-wash). Moreover, five out of the twelve anomalous layers were embedded in age intervals encompassing the dates of major tsunamis that hit eastern Sicily (1908, 1693, and 1169) and the broader Eastern Mediterranean (AD 365 Crete and Santorini at about BP 3600). Seven additional cores were sampled from the northern part of the Augusta Bay, along a transect 60 to 110 m of water depth, to retrieve the details of the MS06 sequence uppermost part. Four out of the seven new cores were selected and studied. Preliminary dating suggests that the sampled sequence spans ca. 400-500 yrs. Moreover, physical properties, ITRAX X-ray fluorescence (XRF) and grain size analyses point out the presence of a peculiar interval made of Posidonia remnants, coarse sand and shell debris on the two cores closer to the shore. The two far-off cores seem to be more homogenous but a few thin sandy lenses enriched of Posidonia remnant were also recognized. Further detailed micropaleontological analysis and corroboration with instrumental data are still in progress and will help in discriminating single events potentially related to tsunami back-was
Conventionally-heated miniaturised furnace for graphitisation of microgram-sized carbon samples
No full textA new type of miniaturized, externally heated graphitization reaction furnace, the microconventional furnace (MCF), was constructed following our development of the laser heated furnace (LHF). The MCF is comprised of a gas reactor, a cold finger cooling system, and a compact resistive heater, which can raise the temperature of the hot finger to 850°C. The gas reactor is provided with three integrated valves to connect with the hydrogen/vacuum manifold, to isolate the reactor, and to connect with sample vessels. We made two types of MCF: the type 1 furnace (volume of 0.9 mL), with an integral stainless steel cold finger, and the type 2 furnace (volume from 1.3 to 10 mL), with a changeable glass cold finger. The MCF is designed for above atmospheric pressure (up to 2500 mbar) operation to decrease the overall graphitization time and improve the carbon yield. The MCF provides an effective solution for producing graphite from carbon dioxide (CO 2 ) sample gas from 5 to 2000 µg of carbon with only 0.083 μg of 100 pMC extraneous carbon added. Cross-contamination tests show that the MCFs have no memory effect from previous samples
Changes in El Niño - Southern Oscillation (ENSO) conditions during the Greenland Stadial 1 (GS-1) chronozone revealed by New Zealand tree-rings
No full textThe warming trend at the end of the last glacial was disrupted by rapid cooling clearly identified in Greenland (Greenland Stadial 1 or GS-1) and Europe (Younger Dryas Stadial or YD). This reversal to glacial-like conditions is one of the best known examples of abrupt change but the exact timing and global spatial extent remain uncertain. Whilst the wider Atlantic region has a network of high-resolution proxy records spanning GS-1, the Pacific Ocean suffers from a scarcity of sub-decadally resolved sequences. Here we report the results from an investigation into a tree-ring chronology from northern New Zealand aimed at addressing the paucity of data. The conifer tree species kauri (Agathis australis) is known from contemporary studies to be sensitive to regional climate changes. An analysis of a ‘historic’ 452-year kauri chronology confirms a tropical-Pacific teleconnection via the El Niño – Southern Oscillation (ENSO). We then focus our study on a 1010-year sub-fossil kauri chronology that has been precisely dated by comprehensive radiocarbon dating and contains a striking ring-width downturn between ∼12,500 and 12,380 cal BP within GS-1. Wavelet analysis shows a marked increase in ENSO-like periodicities occurring after the downturn event. Comparison to low- and mid-latitude Pacific records suggests a coherency with ENSO and Southern Hemisphere atmospheric circulation change during this period. The driver(s) for this climate event remain unclear but may be related to solar changes that subsequently led to establishment and/or increased expression of ENSO across the mid-latitudes of the Pacific, seemingly independent of the Atlantic and polar regions. © 2016, Elsevier Ltd