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  • 1
    Description: Probability density function (PDF) methods are a promising alternative to predicting the transport of solutes in groundwater under uncertainty. They make it possible to derive the evolution equations of the mean concentration and the concentration variance, used in moment methods. A mixing model, also known as a dissipation model, is essential for both methods. Finding a satisfactory mixing model is still an open question and due to the rather elaborate PDF methods, a difficult undertaking. Both the PDF equation and the concentration variance equation depend on the same mixing model. This connection is used to find and test an improved mixing model for the much easier to handle concentration variance. Subsequently, this mixing model is transferred to the PDF equation and tested. The newly proposed mixing model yields significantly improved results for both variance modelling and PDF modelling.
    Keywords: Physics - Fluid Dynamics
    Source: Cornell University
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  • 2
    Language: English
    In: Analele Universităţii "Ovidius" Constanţa. Seria Matematică 2015, 23(3):187-208
    Description: Concentrations of chemical species transported in random environments need to be statistically characterized by probability density functions (PDF). Solutions to evolution equations for the one-point one-time PDF are usually based on systems of computational particles described by It^o equations. We...
    Keywords: Pdf Methods ; Mixing ; Random Walk ; Porous Media
    Source: University of Bergen
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  • 3
    Language: English
    In: Analele Universităţii "Ovidius" Constanţa. Seria Matematică 2015, 23(3):187-208
    Description: Concentrations of chemical species transported in random environments need to be statistically characterized by probability density functions (PDF). Solutions to evolution equations for the one-point one-time PDF are usually based on systems of computational particles described by It^o equations. We...
    Keywords: Pdf Methods ; Mixing ; Random Walk ; Porous Media
    ISSN: 18440835
    E-ISSN: 18440835
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  • 4
    Language: English
    In: Vadose Zone Journal, 2011, Vol.10(3), p.988
    Description: Recent studies have shown that rhizosphere hydraulic properties may differ from those of the bulk soil. Specifically, mucilage at the root-soil interface may increase the rhizosphere water holding capacity and hydraulic conductivity during drying. The goal of this study was to point out the implications of such altered rhizosphere hydraulic properties for soil-plant water relations. We addressed this problem through modeling based on a steady-rate approach. We calculated the water flow toward a single root assuming that the rhizosphere and bulk soil were two concentric cylinders having different hydraulic properties. Based on our previous experimental results, we assumed that the rhizosphere had higher water holding capacity and unsaturated conductivity than the bulk soil. The results showed that the water potential gradients in the rhizosphere were much smaller than in the bulk soil. The consequence is that the rhizosphere attenuated and delayed the drop in water potential in the vicinity of the root surface when the soil dried. This led to increased water availability to plants, as well as to higher effective conductivity under unsaturated conditions. The reasons were two: (i) thanks to the high unsaturated conductivity of the rhizosphere, the radius of water uptake was extended from the root to the rhizosphere surface; and (ii) thanks to the high soil water capacity of the rhizosphere, the water depletion in the bulk soil was compensated by water depletion in the rhizosphere. We conclude that under the assumed conditions, the rhizosphere works as an optimal hydraulic conductor and as a reservoir of water that can be taken up when water in the bulk soil becomes limiting.
    Keywords: Agriculture;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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  • 5
    Language: English
    In: Water Resources Research, 02/2019, Vol.55(2), pp.990-1010
    Description: The improvement of process representations in hydrological models is often only driven by the modelers' knowledge and data availability. We present a comprehensive comparison between two hydrological models of different complexity that is developed to support (1) the understanding of the differences between model structures and (2) the identification of the observations needed for model assessment and improvement. The comparison is conducted on both space and time and by aggregating the outputs at different spatiotemporal scales. In the present study, mHM, a process‐based hydrological model, and ParFlow‐CLM, an integrated subsurface‐surface hydrological model, are used. The models are applied in a mesoscale catchment in Germany. Both models agree in the simulated river discharge at the outlet and the surface soil moisture dynamics, lending their supports for some model applications (drought monitoring). Different model sensitivities are, however, found when comparing evapotranspiration and soil moisture at different soil depths. The analysis supports the need of observations within the catchment for model assessment, but it indicates that different strategies should be considered for the different variables. Evapotranspiration measurements are needed at daily resolution across several locations, while highly resolved spatially distributed observations with lower temporal frequency are required for soil moisture. Finally, the results show the impact of the shallow groundwater system simulated by ParFlow‐CLM and the need to account for the related soil moisture redistribution. Our comparison strategy can be applied to other models types and environmental conditions to strengthen the dialog between modelers and experimentalists for improving process representations in Earth system models. A comprehensive approach is developed to compare states and fluxes simulated by different models at different spatial and temporal scales Different strategies depending on the model output are identified to discriminate between model structures and for modeling improvements The approach strengthens the dialog between modelers and experimentalists for improving process representation in hydrological models
    Keywords: Hydrological Models ; Assessments ; Monitoring Strategies ; Improvements;
    ISSN: 0043-1397
    E-ISSN: 1944-7973
    Source: American Geophysical Union (via CrossRef)
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  • 6
    In: Water Resources Research, February 2019, Vol.55(2), pp.990-1010
    Description: The improvement of process representations in hydrological models is often only driven by the modelers' knowledge and data availability. We present a comprehensive comparison between two hydrological models of different complexity that is developed to support (1) the understanding of the differences between model structures and (2) the identification of the observations needed for model assessment and improvement. The comparison is conducted on both space and time and by aggregating the outputs at different spatiotemporal scales. In the present study, mHM, a process‐based hydrological model, and ParFlow‐CLM, an integrated subsurface‐surface hydrological model, are used. The models are applied in a mesoscale catchment in Germany. Both models agree in the simulated river discharge at the outlet and the surface soil moisture dynamics, lending their supports for some model applications (drought monitoring). Different model sensitivities are, however, found when comparing evapotranspiration and soil moisture at different soil depths. The analysis supports the need of observations within the catchment for model assessment, but it indicates that different strategies should be considered for the different variables. Evapotranspiration measurements are needed at daily resolution across several locations, while highly resolved spatially distributed observations with lower temporal frequency are required for soil moisture. Finally, the results show the impact of the shallow groundwater system simulated by ParFlow‐CLM and the need to account for the related soil moisture redistribution. Our comparison strategy can be applied to other models types and environmental conditions to strengthen the dialog between modelers and experimentalists for improving process representations in Earth system models. A comprehensive approach is developed to compare states and fluxes simulated by different models at different spatial and temporal scales Different strategies depending on the model output are identified to discriminate between model structures and for modeling improvements The approach strengthens the dialog between modelers and experimentalists for improving process representation in hydrological models
    Keywords: Hydrological Models ; Assessments ; Monitoring Strategies ; Improvements
    ISSN: 0043-1397
    E-ISSN: 1944-7973
    Source: John Wiley & Sons, Inc.
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  • 7
    Language: English
    In: Frontiers in Cellular and Infection Microbiology, 01 July 2017, Vol.7
    Description: The Western honey bee (Apis mellifera) is widely used as commercial pollinator in worldwide agriculture and, therefore, plays an important role in global food security. Among the parasites and pathogens threatening health and survival of honey bees are two species of microsporidia, Nosema apis and Nosema ceranae. Nosema ceranae is considered an emerging pathogen of the Western honey bee. Reports on the spread of N. ceranae suggested that this presumably highly virulent species is replacing its more benign congener N. apis in the global A. mellifera population. We here present a 12 year longitudinal cohort study on the prevalence of N. apis and N. ceranae in Northeast Germany. Between 2005 and 2016, a cohort of about 230 honey bee colonies originating from 23 apiaries was sampled twice a year (spring and autumn) resulting in a total of 5,600 bee samples which were subjected to microscopic and molecular analysis for determining the presence of infections with N. apis or/and N. ceranae. Throughout the entire study period, both N. apis- and N. ceranae-infections could be diagnosed within the cohort. Logistic regression analysis of the prevalence data demonstrated a significant increase of N. ceranae-infections over the last 12 years, both in autumn (reflecting the development during the summer) and in spring (reflecting the development over winter) samples. Cell culture experiments confirmed that N. ceranae has a higher proliferative potential than N. apis at 27° and 33°C potentially explaining the increase in N. ceranae prevalence during summer. In autumn, characterized by generally low infection prevalence, this increase was accompanied by a significant decrease in N. apis-infection prevalence. In contrast, in spring, the season with a higher prevalence of infection, no significant decrease of N. apis infections despite a significant increase in N. ceranae infections could be observed. Therefore, our data do not support a general advantage of N. ceranae over N. apis and an overall replacement of N. apis by N. ceranae in the studied honey bee population.
    Keywords: Honey Bee ; Apis Mellifera ; Nosema Spp ; Epidemiology ; Replacement ; Biology
    E-ISSN: 2235-2988
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  • 8
    In: Environmental Microbiology, December 2016, Vol.18(12), pp.4456-4470
    Description: Marine have pronounced capabilities of degrading high molecular weight organic matter such as proteins and polysaccharides. Previously we reported on 76 ‐affiliated fosmids from the North Atlantic Ocean's boreal polar and oligotrophic subtropical provinces. Here, we report on the analysis of further 174 fosmids from the same libraries. The combined, re‐assembled dataset (226 contigs; 8.8 Mbp) suggests that planktonic at the oligotrophic southern station use more peptides and bacterial and animal polysaccharides, whereas at the polar station (East‐Greenland Current) use more algal and plant polysaccharides. The latter agrees with higher abundances of algae and terrigenous organic matter, including plant material, at the polar station. Results were corroborated by in‐depth bioinformatic analysis of 14 polysaccharide utilisation loci from both stations, suggesting laminarin‐specificity for four and specificity for sulfated xylans for two loci. In addition, one locus from the polar station supported use of non‐sulfated xylans and mannans, possibly of plant origin. While peptides likely represent a prime source of carbon for in open oceans, our data suggest that as yet unstudied clades of these have a surprisingly broad capacity for polysaccharide degradation. In particular, laminarin‐specific PULs seem widespread and thus must be regarded as globally important.
    Keywords: Polysaccharides – Analysis;
    ISSN: 1462-2912
    E-ISSN: 1462-2920
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