Browsing by Author "Wilkinson, C"
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- ItemControls on 10Be dilution in catchments affected by coseismic landsliding: a 2016 Kaikōura earthquake case-study(Australian Nuclear Science and Technology Organisation, 2021-11-17) Wilkinson, C; Stahl, T; Jones, K; Fujioka, T; Fink, D; Norton, KPThe 2016 Mw 7.8 Kaikōura earthquake triggered tens of thousands of landslides across the northern Canterbury and southern Marlborough regions in the South Island of Aotearoa New Zealand. The influence of landslides generated by this earthquake on sediment generation, transport and deposition in stream networks has varied across the region and through time — some catchments show significant and near-immediate responses while others show little to no change despite the extensive landsliding. We measured 10Be concentrations in detrital quartz sands over a two-year period in the Conway River catchment, which has a total area of ~475 km2 and had ~13 M m3 of new landslide material liberated from hillslopes during the 2016 Kaikōura earthquake. Samples for 10Be analysis were collected at the rangefront of the Seaward Kaikōura Mountains and near the catchment outlet on three sampling campaigns between 2017-2018. We also carried out a similar sampling regime in the nearby Hurunui catchment, which was unaffected by the 2016 Kaikōura earthquake. Measured 10Be concentrations were converted to basin wide mean denudation rates using accepted GIS-based elevation and shielding programs. Our results indicate that apparent catchment-wide erosion rates in the Conway River (i) did not change through time, (ii) have remained similar to basin mean erosion rates for the Hurunui, (iii) overlap with the range of values for exhumation rates of the region (from previously published low-temperature thermochronology data), and (iv) are influenced in part by selection of grain size. We also compared our 10Be concentrations for the Conway catchment to values derived by modelling mean landslide 10Be concentrations constrained by local production rates, detailed mapping of all landslides across the catchment, area-volume scaling, and landslide-channel connectivity estimates. Our modelling estimates show that the mean 10Be concentrations derived from landslide sediment would have been sufficient to dilute pre-earthquake catchment-wide 10Be values by up to a factor of 3. We explore various landscape and landslide parameters that may explain the mismatch between measured and modelled 10Be and ascertain that the combination of storage, site specific channel connectivity, and landslide geometries/failure mechanisms likely exert first-order controls on in-situ 10Be concentrations following such a large catchment-wide disturbance event. We conclude that using fluvial quartz grains to characterise catchment response to landsliding and the mass balance of earthquakes, is subject to a number of factors that are highly site-specific. © The Authors
- ItemExtensive sequential polymorphic interconversion in the solid state: two hydrates and ten anhydrous phases of hexamidine diisethionate(American Chemical Society, 2019-10-22) Edkins, K; McIntyre, GJ; Wilkinson, C; Kahlenberg, V; Többens, D; Griesser, UJ; Brüning, J; Schmidt, MU; Steed, JWCrystal polymorphism and solvent inclusion are a dominant research area in the pharmaceutical industry and continue to unveil complex systems. Here, we present the solid-state system of hexamidine diisethionate (HDI), an antiseptic drug compound forming a dimorphic dihydrate as well as 10 anhydrous polymorphs. The X-ray and neutron crystal structures of the hydrated crystal forms and related interaction energies show no direct interaction between the cation and water but very strong interactions between cation and anion, and anion and water. This is observed macroscopically as high stability of the hydrate against dehydration by temperature and humidity. The anhydrous polymorphs reveal a rare case of sequential and reversible polymorphic transformations, which are characterized by thermal analysis and variable-temperature powder X-ray diffraction. While most transitions are accompanied by significant structural changes, the low-energy transitions can only be detected as slight changes in the reflection positions with temperature. HDI thus represents a model compound to investigate polymorphic transitions with small structural changes. © 2019 American Chemical Society
- ItemInsights into the crystallisation process from anhydrous, hydrated and solvated crystal forms of diatrizoic acid(Wiley, 2014-11-04) Fucke, K; McIntyre, GJ; Lemée-Cailleau, MH; Wilkinson, C; Edwards, AJ; Howard, JAK; Steed, JWDiatrizoic acid (DTA), a clinically used X-ray contrast agent, crystallises in two hydrated, three anhydrous and nine solvated solid forms, all of which have been characterised by X-ray crystallography. Single-crystal neutron structures of DTA dihydrate and monosodium DTA tetrahydrate have been determined. All of the solid-state structures have been analysed using partial atomic charges and hardness algorithm (PACHA) calculations. Even though in general all DTA crystal forms reveal similar intermolecular interactions, the overall crystal packing differs considerably from form to form. The water of the dihydrate is encapsulated between a pair of host molecules, which calculations reveal to be an extraordinarily stable motif. DTA presents functionalities that enable hydrogen and halogen bonding, and whilst an extended hydrogen-bonding network is realised in all crystal forms, halogen bonding is not present in the hydrated crystal forms. This is due to the formation of a hydrogen-bonding network based on individual enclosed water squares, which is not amenable to the concomitant formation of halogen bonds. The main interaction in the solvates involves the carboxylic acid, which corroborates the hypothesis that this strong interaction is the last one to be broken during the crystal desolvation and nucleation process.© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
- ItemNew insights into an old molecule: Interaction energies of theophylline crystal forms(American Chemical Society, 2012-01-06) Fucke, K; McIntyre, GJ; Wilkinson, C; Henry, M; Howard, JAK; Steed, JWThe asthma therapeutic theophylline exists in at least three anhydrous polymorphs and a monohydrate. The single-crystal X-ray structure of the high-temperature polymorph form I is presented for the first time, and the energetic relationship between forms I and II is investigated using the partial charges and chemical hardness analysis (PACHA) algorithm. It is shown that the interactions in the form I crystal network are stronger, especially the hydrogen bond. The single-crystal neutron structure of the monohydrate demonstrates static disorder of the water molecule as well as dynamic disorder of the methyl groups. PACHA investigations based on the neutron coordinates reveal that the homomeric interactions in this form are stronger than the interaction of the water with the host molecules. The dehydration of the hydrate should thus leave the theophylline network intact, explaining the isomorphic powder X-ray diffractograms of the monohydrate and its dehydrated form III. © 2012 American Chemical Society
- ItemPhotostimulated luminescence properties of neutron image plates(Elsevier, 2016-09) Popov, AI; Zimmermann, J; McIntyre, GJ; Wilkinson, CThe luminescence properties of two commercial neutron-sensitive image-plates based on Gd2O3-doped BaFBr:Eu2+ storage phosphors are examined. These are white Fuji plates and blue Fuji plates (BAS-ND) with Gd2O3 content by weight of 34% and 50%, respectively. Both plates show two maxima in the photostimulation spectrum near 500 nm and 600 nm, with the ratio of the peak responses (I600 nm/I500 nm) 1.39 and 0.53 for the white and blue plates respectively. The optimum wavelengths for photostimulation for the two phosphors are therefore different. The response of the blue plate is only 25% that of the white plate, if each is stimulated at its optimum wavelength. © 2016 Elsevier B.V.