56 research outputs found

    Termolecular proton transfer reactions assisted by ionic hydrogen bond formation: Reactions of aromatic cations with polar molecules

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    We present a new method that applies resonantโ€twoโ€photon ionization to generate reactant ions selectively in the source of a highโ€pressure mass spectrometer (R2PIโ€HPMS) for kinetic and equilibrium studies. Applications to reactions that would be obscured otherwise in a complex system are illustrated in mixtures of benzene with polar solvent molecules (S). We observe a novel type of proton transferreactions from C6H6 +โ€ข to two S molecules where S=CH3CN, CH3OH, C2H5OH and CH3COOC2H5, and from C6H5CH3 +โ€ข to two S molecules where S=CH3OH and C2H5OH to form protonated solvent S2H+ dimers. The reactions are driven by the strong hydrogen bonds in the S2H+ dimers and therefore require the formation of the hydrogen bond concertedly with proton transfer, to make the process energetically feasible. The adducts (C6H6 +โ€ข)S are observed with blocked solvent molecules where the subsequent switching reaction to yield S2H+ is slow, but not with alcohol reactants that can form hydrogenโ€bonded chains that facilitate fast subsequent proton extraction. Correspondingly, kinetic simulations suggest that the mechanism proceeds through (C6H6 +โ€ข)S+Sโ†’S2H++C6H5 โ€ข and C6H6 +โ€ข+2Sโ†’S2H++C6H5 โ€ขreactions, respectively. The rate coefficients of these reactions are in the range 10โˆ’13โˆ’10โˆ’12 cm3โ€‰sโˆ’1 for the reaction through a bimolecular switching channel and in the range 10โˆ’26โˆ’10โˆ’28 cm6โ€‰sโˆ’1 for reaction through a direct termolecular proton extraction mechanism. The relation to energetics and reactant structure is examined

    Comparison of experimentally measured and computational fluid dynamic predicted deposition and deposition uniformity of monodisperse solid particles in the Vitrocellยฎ AMES 48 air-liquid-interface in-vitro exposure system

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    Accurately determining the delivered dose is critical to understanding biological response due to cell exposure to chemical constituents in aerosols. Deposition efficiency and uniformity of deposition was measured experimentally using monodisperse solid fluorescent particles with mass median aerodynamic diameters (MMAD) of 0.51, 1.1, 2.2 and 3.3 ฮผm in the Vitrocellยฎ AMES 48 air-liquid-interface (ALI) in vitro exposure system. Experimental results were compared with computational fluid dynamic, (CFD; using both Lagrangian and Eulerian approaches) predicted deposition efficiency and uniformity for a single row (N = 6) of petri dishes in the Vitrocellยฎ AMES 48 system. The average experimentally measured deposition efficiency ranged from 0.007% to 0.43% for 0.51โ€“3.3 ฮผm MMAD particles, respectively. There was good agreement between average experimentally measured and the CFD predicted particle deposition efficiency, regardless of approach. Experimentally measured and CFD predicted average uniformity of deposition was greater than 45% of the mean for all particle diameters. During this work a new design was introduced by the manufacturer and evaluated using Lagragian CFD. Lagragian CFD predictions showed better uniformity of deposition, but reduced deposition efficiency with the new design. Deposition efficiency and variability in particle deposition across petri dishes for solid particles should be considered when designing exposure regimens using the Vitrocellยฎ AMES 48 ALI in vitro exposure system

    The Anatomy of Memory Politics: A Formalist Analysis of Tate Britainโ€™s โ€˜Artist and Empireโ€™ and the Struggle over Britainโ€™s Imperial Past

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    In this paper, I propose a new approach for understanding the meaning of memory politics, which draws upon the archetypal literary criticism of Northrop Frye. I suggest that the four archetypes elaborated by Fryeโ€”comedy, romance, tragedy, and satireโ€”can be used as a heuristic device for interpreting the contested historical narratives that are associated with the politics of memory. I illustrate this approach through a case-study of Artists and Empire: Facing Britainโ€™s Imperial Past, an exhibition held at Tate Britain in 2016, amidst increasing contestation over the meaning of the British Empire. In sum, I find that the exhibit narrated Britainโ€™s imperial past as a comedy, in which a key theme was the progressive cultural mixing of the British and the people they colonized. To conclude, I discuss the implications of such a narrative for constructing an inclusive, postcolonial British identity. As an alternative, I draw on Aristotle to suggest that a tragic narrative would have been more propitious

    Steps to Prophet Zoroaster with a book of daily Zoroastrian prayers

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