845 research outputs found

    On the Effects of Droplet Loading on the Structure of Spray Jets

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    This paper uses advanced laser diagnostics to investigate the effects of droplet loading on the structure and mixing patterns of sprays in a non-reacting, turbulent jet. A nozzle designed at University of Sydney with the objective of studying spray flames has been used for producing a two phase flow in a co-flowing air stream with well defined boundary conditions. Varying the quantity of liquid injective will vary the number density of the droplets in the flow. The co-flowing air stream is seeded with a fixed concentration of nitric oxide, NO which will act as a conserved scalar. Laser induced fluorescence of NO is exploited to provide a direct quantitative measure of the mixture fraction. Radial profiles of the mean and the rms of mixture fraction has been collected at various axial positions in jets with different spray loadings. It is found that mixture fraction profiles are different from those measured in turbulent gaseous jets and increasing the droplet loading increases the mixture fraction of the jet due to evaporating droplets

    Operator Product Expansion for Exclusive Decays: B^+ ->Ds^+ e+e- and B^+ -> Ds^{*+} e+e-

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    The decays B+Ds,d+e+eB^+\to D_{s,d}^+e^+e^- and B+Ds,d+e+eB^+\to D_{s,d}^{*+}e^+e^- proceed through a weak and an electromagnetic interaction. This is a typical ``long distance'' process, usually difficult to compute systematically. We propose that over a large fraction of phase space a combination of an operator product and heavy quark expansions effectively turns this process into one in which the weak and electromagnetic interactions occur through a local operator. Moreover, we use heavy quark spin symmetry to relate all the local operators that appear in leading order of the operator expansion to two basic ones. We use this operator expansion to estimate the decay rates for B+Ds,d()+e+eB^+\to D_{s,d}^{(*)+}e^+e^-.Comment: 4 pages, 1 figure, Latex, published version in PR

    Aid to conflict-affected countries : lessons for donors

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    The first section looks at the implications of conflict for aid effectiveness and selectivity. We argue that, while aid is generally effective in promoting growth and by implication reducing poverty, it is more effective in promoting growth in post-conflict countries. We then consider the implications of these findings for donor selectivity models and for assessment of donor performance in allocating development aid among recipient countries. We argue that, while further research on aid effectiveness in post-conflict scenarios is needed, existing selectivity models should be augmented with, inter alia, post-conflict variables, and donors should be evaluated on the basis, inter alia, of the share of their aid budgets allocated to countries experiencing post-conflict episodes. We also argue for aid delivered in the form of projects to countries with weak institutions in early post-conflict years. The second section focuses on policies for donors operating in conflict-affected countries. We set out five of the most important principles: (1) focus on broad-based recovery from war; (2) to achieve a broad-based recovery, get involved before the conflict ends; (3) focus on poverty, but avoid &lsquo;wish lists&rsquo;; (4) help to reduce insecurity so aid can contribute more effectively to growth and poverty reduction; and (5) in economic reform, focus on improving public expenditure management and revenue mobilisation. The third section concludes by emphasising the fact that there is no hard or fast dividing line between &lsquo;war&rsquo; and &lsquo;peace&rsquo; and that it may take many years for a society to become truly &lsquo;post&rsquo;-conflict&rsquo;. Donors, therefore, need to prepare for the long haul.<br /

    Molecular Structure and Confining Environment of Sn Sites in Single-Site Chabazite Zeolites

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    Chabazite (CHA) molecular sieves, which are industrial catalysts for the selective reduction of nitrogen oxides and the conversion of methanol into olefins, are also ideal materials in catalysis research because their crystalline frameworks contain one unique tetrahedral-site. The presence of a single lattice site allows for more accurate descriptions of experimental data using theoretical models, and consequently for more precise structure-function relationships of active sites incorporated into framework positions. A direct hydrothermal synthesis route to prepare pure-silica chabazite molecular sieves substituted with framework Sn atoms (Sn-CHA) is developed, which is required to predominantly incorporate Sn within the crystalline lattice. Quantitative titra-tion with Lewis bases (NH3, CD3CN, pyridine) demonstrates that framework Sn atoms behave as Lewis acid sites, which catalyze intermolecular propionaldehyde reduction and ethanol oxidation, as well as glucose-fructose isomerization. Aqueous-phase glucose isomerization turnover rates on Sn-CHA are four orders-of-magnitude lower than on Sn-Beta zeolites, but similar to those on amorphous Sn-silicates. Further analysis of Sn-CHA by dynamic nuclear polarization enhanced solid-state nuclear magnetic reso-nance (DNP NMR) spectroscopy enables measurement of 119Sn NMR chemical shift anisotropy (CSA) of Sn sites. Comparison of experimentally determined CSA parameters to those computed on cluster models using density functional theory supports the pres-ence of closed sites (Sn-(OSi)4) and defect sites ((HO)-Sn-(OSi)3) adjacent to a framework Si vacancy), which respectively be-come hydrated hydrolyzed-open sites and defect sites when Sn-CHA is exposed to ambient conditions or aqueous solution. Kinetic and spectroscopic data show that large substrates (e.g., glucose) are converted only on Sn sites located within disordered mesopo-rous voids of Sn-CHA, which are selectively detected and quantified in IR and 15N and 119Sn DNP NMR spectra using pyridine titrants. This integrated experimental and theoretical approach allows precise description of the primary coordination and secondary confining environments of Sn active sites isolated in crystalline silica frameworks, and clearly establishes the role of confinement within microporous voids for aqueous-phase glucose isomerization catalysis

    Search for flavor-changing neutral currents and lepton-family-number violation in two-body D0 decays

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    Results of a search for the three neutral charm decays, D0 -> mu e, D0 -> mu mu, and D0 -> e e, are presented. This study was based on data collected in Experiment 789 at the Fermi National Accelerator Laboratory using 800 GeV/c proton-Au and proton-Be interactions. No evidence is found for any of the decays. Upper limits on the branching ratios, at the 90% confidence level, are obtained.Comment: 28 pages, 18 figures. Submitted to Physical Review

    Building operational research capacity in the Pacific

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    Operational research (OR) in public health aims to investigate strategies, interventions, tools or knowledge that can enhance the quality, coverage, effectiveness or performance of health systems. Attention has recently been drawn to the lack of OR capacity in public health programmes throughout the Pacific Islands, despite considerable investment in implementation. This lack of ongoing and critical reflection may prevent health programme staff from understanding why programme objectives are not being fully achieved, and hinder long-term gains in public health. The International Union Against Tuberculosis and Lung Disease (The Union) has been collaborating with Pacific agencies to conduct OR courses based on the training model developed by The Union and Médecins Sans Frontières Brussels-Luxembourg in 2009. The first of these commenced in 2011 in collaboration with the Fiji National University, the Fiji Ministry of Health, the World Health Organization and other partners. The Union and the Secretariat of the Pacific Community organised a second course for participants from other Pacific Island countries and territories in 2012, and an additional course for Fijian participants commenced in 2013. Twelve participants enrolled in each of the three courses. Of the two courses completed by end 2013, 18 of 24 participants completed their OR and submitted papers by the course deadline, and 17 papers have been published to date. This article describes the context, process and outputs of the Pacific courses, as well as innovations, adaptations and challenges
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