2,570 research outputs found

    A seamlessly coupled GIS and distributed groundwater flow model

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    Abstract There are three approaches for coupling groundwater models with GISs, i.e. loose, tight, and seamless. In seamless coupling a model code is written into, and run from within, a GIS. We implemented {BGS} {GISGroundwater} in a {GIS} in this way for the first time. It facilitates the construction and simulation of the model, and the visualisation of the results all within the {GIS} environment. The model consists of a 2D finite-difference groundwater flow model and a simple user-interface. It can represent heterogeneous aquifers, variably confined and unconfined conditions, and distributed groundwater recharge and abstraction. It offers benefits in terms of ease of use and in streamlining the model construction and application process. {BGS} {GISGroundwater} has been validated against analytical solutions to groundwater-head profiles for a range of aquifer configurations. This model lowers barriers to entry to groundwater flow modelling for a wider group of environmental scientists

    Parametrisation of the orographic enhancement of precipitation and deposition in a long-term, long-range transport model

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    International audienceOrographic enhancement of wet deposition arising from the 'seeder-feeder' effect is, by necessity, highly parametrised in long-range transport models of acid deposition that are long-term (i.e. annual average) and spatially resolved at tens of kilometres. Here, we describe a mechanistic approach to the incorporation of these mechanisms into such a model. The model formulation required the following: precipitation rate by direction and quantification of the fractions that are orographic and non-orographic; treatment of the fast oxidation of sulfur dioxide in clouds; the directionality of the seeder-feeder process; and a quantitative basis for increasing wet deposition factors to account for the seeder-feeder process. The directionality of non-orographic precipitation was determined from meteorological data at 47 sites across the UK. Orographic precipitation varies on a much finer scale than can be interpolated from measurements, and thus a modelling approach was adopted. The directionality of the seeder-feeder effect was taken from measurements. The enhancement factor of the orographic component of precipitation, assumed to represent feeder-rain, was determined from a review of measurements. Fast oxidation of sulfur dioxide is an observed phenomenon in cap-cloud, but limited in duration. An adjustment was made to the sulfur dioxide oxidation rate in the model in locations where cap-cloud was assumed to be present. The results from the model were compared with UK deposition budgets and enhanced wet deposition maps. The revised parametrisation underestimated the UK wet deposition budgets of oxidised N and S, but spatial patterns of deposition were improved for much of the UK. It was concluded that this was a satisfactory outcome given the constraints of the statistical approach of weighting of deposition at receptors utilising straight line trajectories. The sensitivity of the model to directional constraints of seeder-feeder enhancement was tested and it was concluded that a fairly narrow constraint resulted in similar estimations to a broader one, and the broader constraint was thus adopted as frontal conditions which result in the process arrive from a fairly broad band of directions. When enhancement was allowed to occur from all directions, UK wet deposition of oxidised N and S was increased by 10%. The sensitivity to the enhancement factor on wet deposition was tested and found to be relatively robust. An increase in the enhancement factor from 2 to 6 resulted in increases in UK wet deposition of oxidised N and S of 9 and 6%, respectively.Key words: Atmospheric composition and structure (pollution ? urban and regional) ? Meteorology and atmospheric dynamics (precipitation

    Nonprofit-public collaborations: understanding governance dynamics

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    As many of the challenges facing society are too complex to be addressed by single organizations working alone, nonprofit organizations are increasingly working in collaboration with public authorities. The governance of nonprofit–public collaborations is important for their effectiveness, yet it remains poorly understood. Drawing on case study research, this article examines and develops an extant conceptual model developed by Takahashi and Smutny that seeks to explain the formation and demise of nonprofit collaborations in terms of “collaborative windows” and the inability to adapt initial governance structures. The research finds that while initial governance structures are an important constraint on development, they can be adapted and changed. It also suggests that the development of collaborations is not only influenced by changes in the collaborative window but also by how key actors in the collaboration respond to important internal tensions

    Quantifying water requirements of African ungulates through a combination of functional traits

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    Climate and land use change modify surface water availability in African savannas. Surface water is a key resource for both wildlife and livestock and its spatial and temporal distribution is important for understanding the composition of large herbivore assemblages in savannas. Yet, the extent to which ungulate species differ in their water requirements remains poorly quantified. Here, we infer the water requirements of 48 African ungulates by combining six different functional traits related to physiological adaptations to reduce water loss, namely minimum dung moisture, relative dung pellet size, relative surface area of the distal colon, urine osmolality, relative medullary thickness, and evaporation rate. In addition, we investigated how these differences in water requirements relate to differences in dietary water intake. We observed strong correlations between traits related to water loss through dung, urine and evaporation, suggesting that ungulates minimize water loss through multiple pathways simultaneously, which suggests that each trait can thus be used independently to predict water requirements. Furthermore, we found that browsers and grazers had similar water requirements, but browsers are expected to be less dependent on surface water because they acquire more water through their diet. We conclude that these key functional traits are a useful way to determine differences in water requirements and an important tool for predicting changes in herbivore community assembly resulting from changes in surface water availability

    Emission-line Helium Abundances in Highly Obscured Nebulae

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    This paper outlines a way to determine the ICF using only infrared data. We identify four line pairs, [NeIII] 36\micron/[NeII] 12.8\micron, [NeIII]~15.6\micron /[NeII] 12.8\micron, [ArIII] 9\micron/[ArII] 6.9\micron, and [ArIII] 21\micron/[ArII] 6.9\micron, that are sensitive to the He ICF. This happens because the ions cover a wide range of ionization, the line pairs are not sensitive to electron temperature, they have similar critical densities, and are formed within the He+^+/H+^+ region of the nebula. We compute a very wide range of photoionization models appropriate for galactic HII regions. The models cover a wide range of densities, ionization parameters, stellar temperatures, and use continua from four very different stellar atmospheres. The results show that each line pair has a critical intensity ratio above which the He ICF is always small. Below these values the ICF depends very strongly on details of the models for three of the ratios, and so other information would be needed to determine the helium abundance. The [Ar III] 9\micron/[ArII] 6.9\micron ratio can indicate the ICF directly due to the near exact match in the critical densities of the two lines. Finally, continua predicted by the latest generation of stellar atmospheres are sufficiently hard that they routinely produce significantly negative ICFs.Comment: Accepted by PASP. Scheduled for the October 1999 issue. 11 pages, 5 figure

    Government support for faith-based organizations: the case of a development programme for faith leaders

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    A government initiative to train faith leaders usefully extended existing provision, but will require continuing support for some years. Broader community leadership is not always expected from those holding religious positions. The challenges involved in bridging linguistic and cultural differences highlight some of the reasons why initiatives like this are needed
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