37 research outputs found

    Minimal positive stencils in meshfree finite difference methods for the Poisson equation

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    Meshfree finite difference methods for the Poisson equation approximate the Laplace operator on a point cloud. Desirable are positive stencils, i.e. all neighbor entries are of the same sign. Classical least squares approaches yield large stencils that are in general not positive. We present an approach that yields stencils of minimal size, which are positive. We provide conditions on the point cloud geometry, so that positive stencils always exist. The new discretization method is compared to least squares approaches in terms of accuracy and computational performance.Comment: 26 pages, 20 figure

    Comparative Genomic Studies of Salmonella Heidelberg Isolated From Chicken- and Turkey-Associated Farm Environmental Samples

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    Salmonella is one of the leading causes of human foodborne gastroenteritis in the United States. In addition, Salmonella contributes to morbidity and mortality in livestock. The control of Salmonella is an increasing problematic issue in livestock production due to lack of effective control methods and the constant adaptation of Salmonella to new management practices, which is often related to horizontal acquisition of virulence or antibiotic resistance genes. Salmonella enterica serotype Heidelberg is one of the most commonly isolated serotypes in all poultry production systems in North America. Emergence and persistence of multi-drug resistant Salmonella Heidelberg isolates further impact the poultry production and public health. We hypothesized that distinct poultry production environments affect Salmonella genomic content, and by consequence its survival and virulence abilities. This study compared the genomic composition of S. Heidelberg isolated from environmental samples (19 chicken and 12 turkey isolates) of different breeder farms (16 chicken and 8 turkey farms) in the Midwest, United States. Whole genome comparison of 31 genomes using RAST and SEED identified differences in specific sub-systems in isolates between the chicken- and turkey-associated farm environmental samples. Genes associated with the type IV secretion system (n = 12) and conjugative transfer (n = 3) were absent in turkey farm isolates compared to the chicken ones (p-value < 0.01); Further, turkey farm isolates were enriched in prophage proteins (n = 53; p-value < 0.01). Complementary studies using PHASTER showed that prophages were all Caudovirales phages and were more represented in turkey environmental isolates than the chicken isolates. This study corroborates that isolates from distinct farm environment show differences in S. Heidelberg genome content related to horizontal transfer between bacteria or through viral infections. Complementary microbiome studies of these samples would provide critical insights on sources of these variations. Overall, our findings enhance the understanding of Salmonella genome plasticity and may aid in the development of future effective management practices to control Salmonella

    Defining and assessing industry 4.0 maturity levels–case of the defence sector

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    © 2018, © 2018 Informa UK Limited, trading as Taylor & Francis Group. Firms do not currently fully appreciate the complex characteristics of Industry 4.0 and as a result are uncertain about what it represents for them. In this study, an assessment model is developed to measure the level of implementation of Industry 4.0 technologies, around three dimensions: ‘Factory of the Future’, ‘People and Culture’, and ‘Strategy’. The ‘Factory of the Future’ is the main dimension and is composed of eight attributes: Additive Manufacturing, Cloud, Manufacturing Execution System, Internet of Things and Cyber Physical Systems, Big Data, Sensors, e-Value Chains, and Autonomous Robots. The study uses a defence manufacturing firm to develop, test and validate the model and report on 12 partners. We concluded that the focal firm has an Industry 4.0 maturity level of 59.35, above the sector average of 55.58. This research contributes by empirically developing a model and providing an analysis of major firms in the Defence supply network

    Effects of Pharmaceutical Contamination on Sedment Microbial Communities in Streams

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    The objective of this study was to examine the interaction of pharmaceuticals and personal care products (PPCP) and microbial communities in freshwater ecosystems. This study included two components. The first component consisted of an artificial stream study in which sediment was exposed to environmentally relevant concentrations of three different pharmaceuticals (diphenhydramine, ciprofloxacin, and fluoxetine) individually and as a mixture. Pharmaceutical exposure had no effect on denitrification rates or respiration rates in the sediments, and sediment microbial community composition showed only slight differences between streams dosed with pharmaceuticals and control streams. The second component consisted of a field study in which 5 field sites on 3 different streams were sampled. One stream received no wastewater treatment plant (WWTP) effluent. The two other streams received direct inputs of WWTP effluent, and two sites on each of these streams, one upstream of the effluent point and one downstream, were sampled in order to determine if the effluent was influencing the streams communities. Based on the physical characteristics nitrate, SRP, and temperature, the WWTP effluent affected the stream with the highest effluent input. Microbial communities from both streams demonstrated compositional differences when comparing downstream to upstream sites. One of the microbes that contributed to the composition change is a group that can degrade complex aromatic compounds. Future work will include analysis of antibiotic resistance genes present within the microbial communities and quantification of specific PPCPs in these streams

    Interview with Benjamin Kaiser-Lorentz [2012]

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    Preliminary assessment of the impact of long-term fire treatments on <i>in situ</i> soil hydrology in the Kruger National Park

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    There has been significant attention focused on the impacts of fire frequency and season of burn on ecological processes in the Kruger National Park (KNP). Whilst there has been some examination of these fire effects on soil properties, the explicit linkages of these effects to the hydrology of soils in burnt areas has remained a gap in our understanding. During August 2010, a field scoping campaign was undertaken to assess the impacts, if any, of long-term fire treatments on the hydrology of soils on the experimental burn plots (EBPs) in the KNP. Using various hydrometric and soil physical characterisation instruments soil, hydraulic conductivity and soil strength variations were determined across the extreme fire treatment on the EBPs, the annual August (high fire frequency) plots and the control (no burn) plots, on both the granite and basalt geologies of Pretoriuskop and Satara, respectively. It was found that there were soil hydrological and structural differences to fire treatments on the basalt burn plots, but that these were not as clear on the granite burn plots. In particular, hot, frequent fires appeared to reduce the variation in soil hydraulic conductivity on the annual burn plots on the basalts and led to reduced cohesive soil strength at the surface.Conservation implications: The KNP burn plots are one of the longest running and well studied fire experiments on African savannahs. However, the impacts of fire management on hydrological processes in these water-limited ecosystems remains a gap in our understanding and needs to be considered within the context of climate and land-use changes in the savannah biome.</p
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