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  • 1
    Article
    Article
    Language: English
    In: Vadose Zone Journal, 2016, Vol.15(3), p.0
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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  • 2
    Language: English
    In: Vadose Zone Journal, 2013, Vol.12(3), p.0
    Description: Recent advances in imaging techniques offer the possibility of visualizing the three-dimensional structure of soils at very fine scales. To make use of such information, a thresholding process is commonly implemented to separate the image into solid particles and pores. Despite the multitude of thresholding algorithms available, their performance is being challenged by the complexity of the soil structure. Experience shows that, to improve thresholding performance, existing methods require significant input from a skilled operator, making the thresholding subjective. In this context, this article proposes a new, operator-independent thresholding technique based on the analysis of the intraclass grayscale variance. The method extends the well-established Otsu technique, by applying first a preclassification of the voxels corresponding to the solid phase. Then, a threshold value is determined through minimization of the intraclass variance of the unclassified voxels. The method was implemented globally, then locally for a range of window sizes, with the optimal window size selected as that for which the standardized grayscale variances of the two voxel populations are equal. Results on the three-dimensional soil images investigated suggest that the proposed method performs noticeably better than Otsu's method, and in particular is robust enough to variations in image contrast and soil structure. Tested on a synthetic image, the new method produces a misclassification of only 2% of voxels, compared to 4.9% with Otsu's method. These results suggest that the proposed method can be very useful in the analysis of images of a variety of heterogeneous media, including soils.
    Keywords: Soils ; Algorithms ; Applications ; Complexity ; Computed Tomography Data ; Data Processing ; Dundee Scotland ; Europe ; Experimental Studies ; Great Britain ; Greyscale Imagery ; Imagery ; Mapping ; Matlab ; Micro-Tomography ; Microstructure ; Particulate Materials ; Porosity ; Scotland ; Segmentation ; Soils ; Statistical Analysis ; Synthetic Imagery ; Three-Dimensional Models ; Thresholding Method ; United Kingdom ; Values ; Variance Analysis ; Visualization ; Western Europe ; X-Ray Data;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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  • 3
    Language: English
    In: Vadose Zone Journal, 2004, Vol.3(1), p.262
    Description: As a result of Cryptosporidium parvum in drinking water, several outbreaks of cryptosporidiosis have occurred in the last 10 yr. Although it is generally believed that movement of pathogens through the soil is minimal, recent research has shown that appreciable numbers of C. parvum oocysts may be transported via preferential or fingered flow to groundwater. The objective of the present research was to further investigate and model the transport of oocysts through preferential flow paths in the vadose zone under a "worst-case" scenario. This was studied by adding calves feces containing C. parvum oocysts with a Cl- tracer to undisturbed silt loam columns and disturbed sand columns during a simulated steady-state rain. The sand columns exhibited preferential flow in the form of fingers whereas macropore flow occurred in the undisturbed cores. In the columns with fingered flow, oocysts and Cl were transported rapidly with the same velocity through the columns. Although only 14 to 86% of the amount applied, the number of oocysts transported across the columns was several orders of magnitude above an infective dose. The macropore columns had only a very limited breakthrough of oocysts, which appeared several pore volumes after the Cl broke through initially. A simulation model for the transport of oocysts via preferential flow was developed on the basis of an existing preferential flow model for nonadsorbing solutes, with addition of a first-order sink term for adsorbance of the C. parvum to the air-water-solid (AWS) interfaces, and with velocity and dispersivity parameters derived from Cl- transport. The breakthrough of C. parvum oocysts could be described realistically for the sand columns. However, the model could not describe oocyst transport in the columns with macropores. ; Includes references
    Keywords: Soil Transport Processes ; Sand ; Vadose Zone ; Soil Pollution ; Mathematical Models ; Simulation Models ; Silt Loam Soils ; Preferential Flow ; Oocysts ; Feces ; Calves ; Cryptosporidium Parvum;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
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  • 4
    Language: English
    In: Vadose Zone Journal, 2005, Vol.4(4), p.957
    Keywords: Soils ; Advection ; Air-Water-Solid Interface ; Clastic Sediments ; Colloidal Materials ; Drainage ; Errors ; Evaporation ; Experimental Studies ; Microstructure ; Moisture ; Porosity ; Retention ; Sand ; Saturation ; Scale Factor ; Sediments ; Soils ; Transport ; Unsaturated Zone ; Visualization;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
    Library Location Call Number Volume/Issue/Year Availability
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  • 5
    Language: English
    In: Vadose Zone Journal, 2004, Vol.3(2), p.736
    Description: As a result of Cryptosporidium parvum in drinking water, several outbreaks of cryptosporidiosis have occurred in the last 10 yr. Although it is generally believed that movement of pathogens through the soil is minimal, recent research has shown that appreciable numbers of C. parvum oocysts may be transported via preferential or fingered flow to groundwater. The objective of the present research was to further investigate and model the transport of oocysts through preferential flow paths in the vadose zone under a "worst-case" scenario. This was studied by adding calves feces containing C. parvum oocysts with a Cl- tracer to undisturbed silt loam columns and disturbed sand columns during a simulated steady-state rain. The sand columns exhibited preferential flow in the form of fingers whereas macropore flow occurred in the undisturbed cores. In the columns with fingered flow, oocysts and Cl were transported rapidly with the same velocity through the columns. Although only 14 to 86% of the amount applied, the number of oocysts transported across the columns was several orders of magnitude above an infective dose. The macropore columns had only a very limited breakthrough of oocysts, which appeared several pore volumes after the Cl broke through initially. A simulation model for the transport of oocysts via preferential flow was developed on the basis of an existing preferential flow model for nonadsorbing solutes, with addition of a first-order sink term for
    Keywords: Agriculture;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Library Location Call Number Volume/Issue/Year Availability
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