1,376 research outputs found

    Residence Time Distributions for Turbulent, Critical and Laminar Pipe Flow

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    Longitudinal dispersion processes are often described by the Advection Dispersion Equation (ADE), which is analogous to Fick’s law of diffusion, where the impulse response function of the spatial concentration distribution is assumed to be Gaussian. This paper assesses the validity of the assumption of a Gaussian impulse response function, using Residence Time Distributions (RTDs) obtained from new laboratory data. Measured up- and down-stream temporal concentration profiles have been deconvolved to numerically infer RTDs for a range of turbulent, critical and laminar pipe flows. It is shown that the Gaussian impulse response function provides a good estimate of the system’s mixing characteristics for turbulent and critical flows, and an empirical equation to estimate the dispersion coefficient for Reynolds Number, Re, between 3,000 and 20,000 is presented. For laminar flow, here identified as Re < 3000, the RTDs do not conform to the Gaussian assumption due to insufficient time being available for the solute to become cross-sectionally well mixed. For this situation, which occurs commonly in water distribution networks, a theoretical RTD for laminar flow that assumes no radial mixing is shown to provide a good approximation of the system’s mixing characteristics at short times after injection

    Emerald and Aquamarine Mineralization in Canada

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    This paper reviews the geology, mineralogy, and origin of the gem varieties of beryl, including emerald (green) and aquamarine (blue); it focuses on western Canada, especially the Yukon Territory, because this is where most of the recent discoveries have been made. However, emerald occurrences in Ontario are also considered, including Canada's first reported discovery in 1940. Beryl (B3Al2Si6O18) is relatively common and spatially associated with granites and granitic pegmatites, but emerald is rare because trace amounts of Cr and/or V are required (to replace Al in the crystal structure) and these elements generally do not occur in sufficient concentrations in granitic rocks. The geological conditions needed to bring Be into contact with Cr and/or V are briefly discussed, as are the factors to consider and techniques to use in exploring for gem-quality beryl. SUMMAIRE Le prĂ©sent article traite de la gĂ©ologie, de la minĂ©ralogie et de l'origine de variĂ©tĂ©s gemmifĂšres de bĂ©ryl (vert), dont l'Ă©meraude et l'aigue-marine (bleue). Il traite principalement de l'Ouest canadien, particuliĂšrement du Territoire du Yukon, rĂ©gion oĂč la plupart des dĂ©couvertes ont eu lieu. Toutefois, des dĂ©couvertes faites en Ontario sont aussi considĂ©rĂ©es, incluant la premiĂšre au Canada, en 1940. Le BĂ©ryl (B3Al2Si6O18) est relativement commun et associĂ© aux granites et aux pegmatites granitiques, mais l'Ă©meraude est rare parce qu'elle nĂ©cessite le remplacement de l'Al dans la structure cristalline du bĂ©ryl par du Cr et/ou du V, et ces Ă©lĂ©ments ne se retrouvent gĂ©nĂ©ralement pas dans en concentrations suffisantes dans les roches granitiques. Les facteurs gĂ©ologiques nĂ©cessaires pour que le Be et le Cr et/ou le V soient mis en contact font l'objet de discussion, tout comme les facteurs Ă  considĂ©rer et les techniques Ă  employer dans l'exploration de gisements de bĂ©ryls gemmifĂšres

    The ‘caged torch procession’: Celebrities, protesters and the 2008 Olympic torch relay in London, Paris and San Francisco

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    Along with the opening and closing ceremonies, one of the major non-sports events associated with the modern Olympic Games is the torch relay. Although initiated in 1936, the relay has been subject to relatively little academic scrutiny. The events of April 2008 however will have cast a long shadow on the practice. This essay focuses primarily on one week (6–13 April) in the press coverage of the 2008 torch relay as the flame made its way from London to Paris in Europe and then to San Francisco in the USA. It discusses the interpretations offered in the mediated coverage about the relay, the Olympic movement, the host city and the locations where the relay was taking place, and critically analyses the role of agencies, both for and against the Olympics, that framed the ensuing debate

    A CFD-based mixing model for vegetated flows

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    This paper provides a CFD‐based modelling framework for predicting flow field, turbulence and mixing characteristics within vegetated environments such as ponds and wetlands. The framework has been implemented within a commercial CFD code – ANSYS Fluent 19 – via a set of user‐defined‐functions. Following the approach outlined by King et al. (2012), the standard k‐Δ turbulence closure model has been modified to capture the energy transfer at the vegetation/clear flow shear interface and within the vegetation. The implementation assumes that vegetation is vertical, but non‐orthogonal flow in the horizontal plane is accounted for. Values for the drag coefficient and the mixing coefficients are estimated based on the vegetation stem diameter and density. Following Tanino and Nepf (2008), a switch has been incorporated to account for the fact that the relevant length scale changes from stem diameter to stem spacing as stem density increases. A set of model parameters is proposed, based on a re‐evaluation of previously published laboratory data and theoretical analysis. Five different experimental data sets are used to demonstrate that the model is able to predict mixing within fully‐vegetated systems and due to both vertical and horizontal shear layers. The framework was developed to provide a practical prediction tool for engineering purposes, in particular for the estimation of residence time distributions in real partially‐vegetated stormwater management ponds. Its implementation here within a commercial CFD package potentially facilitates application to complex pond geometries, including patches of different types of vegetation with different bulk stem diameter and density characteristics

    Couplings of light I=0 scalar mesons to simple operators in the complex plane

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    The flavour and glue structure of the light scalar mesons in QCD are probed by studying the couplings of the I=0 mesons σ(600)\sigma(600) and f0(980)f_0(980) to the operators qˉq\bar{q}q, αsG2\alpha_s G^2 and to two photons. The Roy dispersive representation for the ππ\pi\pi amplitude t00(s)t_0^0(s) is used to determine the pole positions as well as the residues in the complex plane. On the real axis, t00t_0^0 is constrained to solve the Roy equation together with elastic unitarity up to the K\Kbar threshold leading to an improved description of the f0(980)f_0(980). The problem of using a two-particle threshold as a matching point is discussed. A simple relation is established between the coupling of a scalar meson to an operator jSj_S and the value of the related pion form-factor computed at the resonance pole. Pion scalar form-factors as well as two-photon partial-wave amplitudes are expressed as coupled-channel Omn\`es dispersive representations. Subtraction constants are constrained by chiral symmetry and experimental data. Comparison of our results for the qˉq\bar{q}q couplings with earlier determinations of the analogous couplings of the lightest I=1 and I=1/2I=1/2 scalar mesons are compatible with an assignment of the σ\sigma, Îș\kappa, a0(980)a_0(980), f0(980)f_0(980) into a nonet. Concerning the gluonic operator αsG2\alpha_s G^2 we find a significant coupling to both the σ\sigma and the f0(980)f_0(980).Comment: 31 pages, 5 figure

    The British Government, Ernest Shackleton, and the rescue of the Imperial Trans-Antarctic Expedition

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    The remarkable rescue of Shackleton's men from Elephant Island, after the sinking of Endurance, and from Ross Island, has been recounted many times by both participants and historians. There has been little critical examination of the part played by governments, nor assessment of some of Shackleton's own actions. In this paper we explore more fully from official British archival sources the extent to which the British Government was prepared to underwrite the rescue efforts; the importance of the plea made by Emily Shackleton directly to the Prime Minister; the role and actions of the Relief Advisory Committee (especially in respect of limiting Shackleton's actions); the significance of the media rights to the debt-laden expedition, and how such preoccupation could have influenced Shackleton's endeavour to rescue his marooned parties

    The BES f_0(1810): a new glueball candidate

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    We analyze the f_0(1810) state recently observed by the BES collaboration via radiative J/\psi decay to a resonant \phi\omega spectrum and confront it with DM2 data and glueball theory. The DM2 group only measured \omega\omega decays and reported a pseudoscalar but no scalar resonance in this mass region. A rescattering mechanism from the open flavored KKbar decay channel is considered to explain why the resonance is only seen in the flavor asymmetric \omega\phi branch along with a discussion of positive C parity charmonia decays to strengthen the case for preferred open flavor glueball decays. We also calculate the total glueball decay width to be roughly 100 MeV, in agreement with the narrow, newly found f_0, and smaller than the expected estimate of 200-400 MeV. We conclude that this discovered scalar hadron is a solid glueball candidate and deserves further experimental investigation, especially in the K-Kbar channel. Finally we comment on other, but less likely, possible assignments for this state.Comment: 11 pages, 4 figures. Major substantive additions, including an ab-initio, QCD-based computation of the glueball inclusive decay width, evaluation of final state effects, and enhanced discussion of several alternative possibilities. Our conclusions are unchanged: the BES f_0(1810) is a promising glueball candidat

    Unitarized Chiral Perturbation Theory in a finite volume: scalar meson sector

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    We develop a scheme for the extraction of the properties of the scalar mesons f0(600), f0(980), and a0(980) from lattice QCD data. This scheme is based on a two-channel chiral unitary approach with fully relativistic propagators in a finite volume. In order to discuss the feasibility of finding the mass and width of the scalar resonances, we analyze synthetic lattice data with a fixed error assigned, and show that the framework can be indeed used for an accurate determination of resonance pole positions in the multi-channel scattering.Comment: 15 pages, 17 figure

    Children’s and parents’ involvement in care order proceedings: a cross-national comparison of judicial decision-makers’ views and experiences

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    This paper presents the views of judicial decision-makers (n= 1794) in four child protection jurisdictions (England, Finland, Norway, and the USA (California)), about whether parents and children are provided with appropriate opportunities to participate in proceedings in their countries. Overall, the study found a high degree of agreement within and between the countries as regards the important conditions for parents and children®s involvement, although the four systems themselves are very different. There was less agreement about children’s involvement than parents’, and the court decision-makers from Norway and Finland were more likely to express doubts about this. Nevertheless, the main message from the judicial decision-makers is that they are relatively satisfied as to how parents and children®s involvement is handled in their countries. Whether or not this confidence is justified, the emphasis on achieving effective involvement of children and parents in court proceedings is likely to grow, with major implications for the workers, decision-makers and agencies involved

    A Classification of Hyper-heuristic Approaches

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    The current state of the art in hyper-heuristic research comprises a set of approaches that share the common goal of automating the design and adaptation of heuristic methods to solve hard computational search problems. The main goal is to produce more generally applicable search methodologies. In this chapter we present and overview of previous categorisations of hyper-heuristics and provide a unified classification and definition which captures the work that is being undertaken in this field. We distinguish between two main hyper-heuristic categories: heuristic selection and heuristic generation. Some representative examples of each category are discussed in detail. Our goal is to both clarify the main features of existing techniques and to suggest new directions for hyper-heuristic research
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