Speciation of Arsenic Using Chelation Solvent Extraction and High Performance Liquid Chromatography     

Shamil J. Cathum  Carl E. Brown  Alison Obenauf  Monique Punt 《洁净——土壤、空气、水》2007,35(1):71-80

Research interest in speciation of arsenic stems from its species dependent behavior in the environment and in living organisms. The complexity of the matrix to be analyzed and low concentrations of target arsenic species that may be labile or difficult to chromatogram, indicate that a suitable pre‐treatment methodology is required. This study investigated the usefulness of chelation solvent extraction – high performance liquid chromatography (CSE‐HPLC) for the speciation of arsenic in water. It involved reacting arsenic with the chelant known for its affinity towards arsenic, followed by extraction, separation, and identification of the arsenic‐chelant‐arsenic complex. Arsenic species having different physicochemical properties were investigated. Species, such as, As₂O₃, As₃O₅, KH₂AsO₄, Na₂HAsO₄, and NaAsO₂ were detected as a group of closely eluted peaks with different retention times and spectral properties, whereas, the organic arsenic species CH₃Na₂AsO₃, o‐arsanilic acid, roxarson and triphenyl arsine separated quite well on the EnviroseP‐CM HPLC column. Key method parameters, such as, type of HPLC column, composition of mobile phase and organic solvents affecting peak resolution and sensitivity were optimized. Real environmental matrices contaminated with arsenic were analyzed under varying wavelengths (λ_max = 190, 210, 220, 234, 244, and 282 nm), with good precision. Different arsenic species were detected in these samples with excellent background and signal‐to‐noise ratios demonstrating the robustness of the method. The detection limit, reproducibility, selectivity, accuracy, and dynamic range of the calibration curves were evaluated.  相似文献   

Distribution and cycling of dimethylsulfide,dimethylsulfoniopropionate, and dimethylsulfoxide during spring and early summer in the Southern Ocean south of New Zealand     

Ronald P. Kiene  David J. Kieber  Doris Slezak  Dierdre A. Toole  Daniela A. del Valle  John Bisgrove  Jordan Brinkley  Alison Rellinger 《Aquatic Sciences - Research Across Boundaries》2007,69(3):305-319

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IGU Commission of the Geography of Tourism and Leisure     

B. Barbier  Alison Arnott  Jon Best  Brian Duffield  Sue Walker 《GeoJournal》1982,6(2):193-193

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Influence Diagrams for Representing Uncertainty in Climate-Related Propositions     

Jim Hall  Craig Twyman  Alison Kay 《Climatic change》2005,69(2-3):343-365

In order to respond to policy questions about the potential impacts of climate change it is usually necessary to assemble large quantities of evidence from a variety of sources. Influence diagrams provide a formal mechanism for structuring this evidence and representing its relationship with the climate-related question of interest. When populated with probabilistic measures of belief an influence diagram provides a graphical representation of uncertainty, which can help to synthesize complex and contentious arguments into a relatively simple, yet evidence-based, graphical output.Following unusually damaging floods in October–November 2000 the UK government commissioned research with a view to establishing the extent to which the floods were a manifestation of hydrological climate change. By way of example application, influence diagrams have been used to represent the evidential reasoning and uncertainties in responding to this question. Three alternative approaches to the mathematization of uncertainty in influence diagrams are demonstrated and compared. In situations of information scarcity and imprecise expert judgements, methods based on interval probabilities have proved to be attractive. Interval probabilities can, it is argued, represent ambiguity and ignorance in a more satisfactory manner than the conventional Bayesian alternative. The analysis provides a quantified commentary on the uncertainties in the conclusion that the events of October–November 2000 were extreme, but cannot in themselves be attributed to climate change.  相似文献   

Towards establishing criteria for identifying trigger mechanisms for soft-sediment deformation: a case study of Late Pleistocene lacustrine sands and clays, Onikobe and Nakayamadaira Basins, northeastern Japan   总被引：1，自引：1，他引：0  

Alison P. Jones  & Kunio Omoto 《Sedimentology》2000,47(6):1211-1226

Five main deformation units, discrete sheets of deformed sediments that lie between a significant thickness of undeformed sediment, were selected for study within Late Pleistocene lacustrine sands and clays in the Onikobe and Nakayamadaira Basins, northeastern Japan. The deformed units show evidence of deformation by a variety of mechanisms including fluidization, liquefaction, brittle failure and cohesive flow. Driving forces are thought to be primarily reverse density gradient systems, but also include gravitational body force, shear stress and unequal loading. The main trigger mechanisms are firstly earthquakes, secondly overloading from volcanic sands and thirdly, to a lesser extent, subaqueous currents. Consideration is given to criteria that allow the trigger mechanism to be identified. This study shows that the following criteria can be used to identify a seismic triggering agent: (i) setting; (ii) the extent of the deformation units; (iii) absence of evidence relating to other potential trigger mechanisms; and (iv) evidence relating to other potential trigger mechanisms is present but can be seen elsewhere in the stratigraphic section associated with undeformed sediment. Conversely, the following criteria, while they are important in interpreting the driving force and deformation mechanism, have no relevance to the trigger mechanism: (i) sediment composition; (ii) deformation structures being restricted to a single stratigraphic interval (<1 m thick) (not necessarily correlatable over large areas); and (iii) similarity to structures in the literature.  相似文献   

Experimental study of the dehydration of 10-Å phase,with implications for its H<Subscript>2</Subscript>O content and stability in subducted lithosphere     

Alison R. Pawley  Nicholas J. Chinnery  Simon M. Clark  Michael J. Walter 《Contributions to Mineralogy and Petrology》2011,162(6):1279-1289

The 10-Å phase (TAP) is a hydrous magnesium silicate that forms from the reaction of talc with H₂O at high pressures. Its high-pressure, low-temperature stability means that it could be a storage site for H₂O in subduction zones. We have determined the position of the TAP dehydration reaction, TAP = enstatite + coesite + H₂O, in phase-equilibrium experiments from 5.0 to 7.1 GPa. Because previous studies had suggested that the composition of TAP is a function of synthesis duration, we used a TAP sample that was synthesised for 392 h. Over the pressure interval of our experiments, the dehydration reaction is isothermal, occurring at a temperature of ~690°C. It is coincident, within experimental uncertainty, with the position of the dehydration reaction of TAP synthesised in short experiments (up to 46 h). Above 7.5 GPa, TAP breaks down to enstatite + stishovite + H₂O. This reaction has a negative dP/dT and terminates at an invariant point involving the 3.65-Å phase at ~9.5 GPa, 500°C. The zero volume change implied by the isothermal reaction TAP = enstatite + coesite + H₂O was used to calculate the interlayer H₂O content of TAP along the reaction. A best-fit H₂O content of 1 H₂O pfu was obtained. This H₂O content is independent of TAP synthesis conditions, suggesting that variations in previously measured H₂O contents of TAP occur during quenching and decompression of the samples. The stability of TAP in the Earth is probably limited to cold subduction zones, but in these, it could persist to 300 km depth.  相似文献   

A photometric and spectroscopic study of the hottest pulsating extreme helium star, V2076 Oph (HD 160641)     

D. J. Wright  A. E. Lynas-Gray  D. Kilkenny  P. L. Cottrell  R. R. Shobbrook  C. Koen  F. W. van Wyk  P. M. Kilmartin  P. Martinez  A. C. Gilmore 《Monthly notices of the Royal Astronomical Society》2006,369(4):2049-2058

We present results from a three-site photometric and high-resolution spectroscopic campaign on the hottest known extreme helium star V2076 Oph (HD 160641). A core programme of intensive observations covered two weeks and a much lower sampling rate extended over another two months. Despite the fact that the data seem to indicate periodicity near half a day (though the light curves are clearly not formed by a single periodicity), conventional Fourier analysis of the data fails to reveal coherent frequencies. Furthermore, we are unable to recover frequencies which were apparently clear in an earlier campaign on the star. Evidence of monotonic pulsation amplitude changes is seen at the higher frequencies from a wavelet analysis, but more data are needed before this study can be extended to lower frequencies. The application of linear stochastic differential equation (LSDE) methods indicates that the observed light variations could be a result of random variations giving the appearance of intermittent periodicity. High-resolution spectroscopic observations were obtained during the campaign and additional observations were made three years later. Complex line profile variations were observed. It is proposed that the different behaviour of the emission line studied may indicate it is associated with a stellar wind or resident circumstellar material. The frequencies that are extracted from the velocity data do not conform to those identified in the current or previous photometric campaigns.  相似文献   

Asteroseismology of the β Cephei star ν Eridani – I. Photometric observations and pulsational frequency analysis     

G. Handler  R. R. Shobbrook †  M. Jerzykiewicz  K. Krisciunas  T. Tshenye  E. Rodríguez  V. Costa  A.-Y. Zhou  R. Medupe  W. M. Phorah  R. Garrido  P. J. Amado  M. Paparó  D. Zsuffa  L. Ramokgali  R. Crowe  N. Purves  R. Avila  R. Knight  E. Brassfield  P. M. Kilmartin  P. L. Cottrell 《Monthly notices of the Royal Astronomical Society》2004,347(2):454-462

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Simplifying the interpretation of continuous time models for spatio-temporal networks     

Gadd  Sarah C.  Comber  Alexis  Gilthorpe  Mark S.  Suchak  Keiran  Heppenstall  Alison J. 《Journal of Geographical Systems》2022,24(2):171-198

Autoregressive and moving average models for temporally dynamic networks treat time as a series of discrete steps which assumes even intervals between data measurements and can introduce bias if this assumption is not met. Using real and simulated data from the London Underground network, this paper illustrates the use of continuous time multilevel models to capture temporal trajectories of edge properties without the need for simultaneous measurements, along with two methods for producing interpretable summaries of model results. These including extracting ‘features’ of temporal patterns (e.g. maxima, time of maxima) which have utility in understanding the network properties of each connection and summarising whole-network properties as a continuous function of time which allows estimation of network properties at any time without temporal aggregation of non-simultaneous measurements. Results for temporal pattern features in the response variable were captured with reasonable accuracy. Variation in the temporal pattern features for the exposure variable was underestimated by the models. The models showed some lack of precision. Both model summaries provided clear ‘real-world’ interpretations and could be applied to data from a range of spatio-temporal network structures (e.g. rivers, social networks). These models should be tested more extensively in a range of scenarios, with potential improvements such as random effects in the exposure variable dimension.

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On the distribution of GPS signal amplitudes during low-latitude ionospheric scintillation     

Alison de Oliveira Moraes  Eurico Rodrigues de Paula  Waldecir João Perrella  Fabiano da Silveira Rodrigues 《GPS Solutions》2013,17(4):499-510

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