37,256 research outputs found

    Ion-retarding lens improves the abundance sensitivity of tandem mass spectrometers

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    Ion-retarding lens which increases the abundance sensitivity of tandem magnetic-analyzer mass spectrometers measures isotopes of low abundance in mass positions adjacent to isotopes of high abundance. The lens increases the abundance sensitivity for isotopes lying farther from high abundance isotopes than the energy cutoff of the lens

    National Evaluation of the Capacity Building Programme in English Local Government: Annex 3. Direct Support in Poor and Weak Local Authorities: Emerging findings

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    This report summarises emerging findings from initial scoping analysis and case study fieldwork with authorities that have received Direct Support from the Capacity Building Programme (CBP) for local government. The report is one of a series of outputs from the national evaluation of the CBP, being undertaken by a team of researchers at the Policy Research Institute (PRI) at Leeds Metropolitan University and the Cities Research Unit at the University of West of England

    Heat transport and flow structure in rotating Rayleigh-B\'enard convection

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    Here we summarize the results from our direct numerical simulations (DNS) and experimental measurements on rotating Rayleigh-B\'enard (RB) convection. Our experiments and simulations are performed in cylindrical samples with an aspect ratio \Gamma varying from 1/2 to 2. Here \Gamma=D/L, where D and L are the diameter and height of the sample, respectively. When the rotation rate is increased, while a fixed temperature difference between the hot bottom and cold top plate is maintained, a sharp increase in the heat transfer is observed before the heat transfer drops drastically at stronger rotation rates. Here we focus on the question of how the heat transfer enhancement with respect to the non-rotating case depends on the Rayleigh number Ra, the Prandtl number Pr, and the rotation rate, indicated by the Rossby number Ro. Special attention will be given to the influence of the aspect ratio on the rotation rate that is required to get heat transport enhancement. In addition, we will discuss the relation between the heat transfer and the large scale flow structures that are formed in the different regimes of rotating RB convection and how the different regimes can be identified in experiments and simulations.Comment: 12 pages, 10 figure

    A concurrent precursor inflow method for Large Eddy Simulations and applications to finite length wind farms

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    In order to enable simulations of developing wind turbine array boundary layers with highly realistic inflow conditions a concurrent precursor method for Large Eddy Simulations is proposed. In this method we consider two domains simultaneously, i.e. in one domain a turbulent Atmospheric Boundary Layer (ABL) without wind turbines is simulated in order to generate the turbulent inflow conditions for a second domain in which the wind turbines are placed. The benefit of this approach is that a) it avoids the need for large databases in which the turbulent inflow conditions are stored and the correspondingly slow I/O operations and b) we are sure that the simulations are not negatively affected by statically swept fixed inflow fields or synthetic fields lacking the proper ABL coherent structures. Sample applications are presented, in which, in agreement with field data a strong decrease of the power output of downstream wind-turbines with respect to the first row of wind-turbines is observed for perfectly aligned inflow.Comment: 13 pages, 5 figure

    Radial boundary layer structure and Nusselt number in Rayleigh-Benard convection

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    Results from direct numerical simulations for three dimensional Rayleigh-Benard convection in a cylindrical cell of aspect ratio 1/2 and Pr=0.7 are presented. They span five decades of Ra from 2×1062\times 10^6 to 2×10112 \times10^{11}. Good numerical resolution with grid spacing ∼\sim Kolmogorov scale turns out to be crucial to accurately calculate the Nusselt number, which is in good agreement with the experimental data by Niemela et al., Nature, 404, 837 (2000). In underresolved simulations the hot (cold) plumes travel further from the bottom (top) plate than in the fully resolved case, because the thermal dissipation close to the sidewall (where the grid cells are largest) is insufficient. We compared the fully resolved thermal boundary layer profile with the Prandtl-Blasius profile. We find that the boundary layer profile is closer to the Prandtl Blasius profile at the cylinder axis than close to the sidewall, due to rising plumes in that region.Comment: 10 pages, 6 figure

    Sidewall effects in Rayleigh-B\'enard convection

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    We investigate the influence of the temperature boundary conditions at the sidewall on the heat transport in Rayleigh-B\'enard (RB) convection using direct numerical simulations. For relatively low Rayleigh numbers Ra the heat transport is higher when the sidewall is isothermal, kept at a temperature Tc+Δ/2T_c+\Delta/2 (where Δ\Delta is the temperature difference between the horizontal plates and TcT_c the temperature of the cold plate), than when the sidewall is adiabatic. The reason is that in the former case part of the heat current avoids the thermal resistance of the fluid layer by escaping through the sidewall that acts as a short-circuit. For higher Ra the bulk becomes more isothermal and this reduces the heat current through the sidewall. Therefore the heat flux in a cell with an isothermal sidewall converges to the value obtained with an adiabatic sidewall for high enough Ra (≃1010\simeq 10^{10}). However, when the sidewall temperature deviates from Tc+Δ/2T_c+\Delta/2 the heat transport at the bottom and top plates is different from the value obtained using an adiabatic sidewall. In this case the difference does not decrease with increasing Ra thus indicating that the ambient temperature of the experimental apparatus can influence the heat transfer. A similar behavior is observed when only a very small sidewall region close to the horizontal plates is kept isothermal, while the rest of the sidewall is adiabatic. The reason is that in the region closest to the horizontal plates the temperature difference between the fluid and the sidewall is highest. This suggests that one should be careful with the placement of thermal shields outside the fluid sample to minimize spurious heat currents.Comment: 27 pages, 16 figure

    National Evaluation of the Capacity Building Programme in English Local Government: Annex 4: Follow On Study of Progress in Seven Case Study Improvement Partnerships

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    This report is one of a series of outputs from the national evaluation of the Capacity Building Programme for local government in England (CBP), being undertaken by a team of researchers at the Policy Research Institute (PRI) at Leeds Metropolitan University and the Cities Research Unit at the University of West of England. This report summarises the findings from the second phase of fieldwork with regional and sub-regional Improvement Partnerships, established to facilitate capacity building and improvement activity in local authorities. The research underpinning this report was undertaken in seven case study Improvement Partnerships (see Section 2) in October and November 2006 and follows a similar – baseline – exercise undertaken during the same period during 2005. It thus both draws on the earlier research (see Section 3) and identifies evidence of progress and impact (see Section 10) since the baseline phase

    National Evaluation of the Capacity Building Programme in English Local Government: Annex 1. Seven Case Studies: The Pilot Programme

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    This report presents the findings of the evaluation of the Capacity Building pilots. The evaluation of the pilots is part of the on-going evaluation of the Capacity Building Programme and has been undertaken in the early scoping phase of the main evaluation in order to capture key learning points and insights into the programme. It is intended that the ongoing evaluation of the Capacity Building Programme will be formative and assist in the development of the programme over time. In what follows the background to the pilots programme is discussed, highlighting the kinds of capacity building activities the pilots are engaged with and the link between the Capacity Building Programme and the CPA. The report outlines the structure and purpose of the pilots programme and the nature and characteristics of the different pilots that were undertaken. The seven case studies are then discussed in more detail in the main body of 1 Introduction | 5 the report. These are drawn together in key themes and findings which can be used to strengthen future project development
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