1,720,984 research outputs found
Neutron tomography data collected with MCP detector (soil specimen)
No full textNeutron tomography data collected with MCP detector in July 2016 at the ISIS Neutron Spallation Source, UK as part of the scientific commissioning of the neutron imaging beamline, IMAT. Different projection angles were acquired over an angular range of 180° (first 41 projections with angular step of 3° and the last 14 projections with angular step of 4°).</span
X-ray Computed Tomography and image-based modelling of plant, root and soil systems, for better understanding of phosphate uptake
No full textA major constraint to crop growth is the poor bioavailability of edaphic nutrients, especially phosphate (P). Improving the nutrient acquisition efficiency of crops is crucial in addressing pressing global food-security issues arising from increasing world population, reduced fertile land and changes in the climate. Despite the undoubted importance of root architecture and root/soil interactions to nutrient uptake, there is a lack of approaches for quantifying plant roots non-invasively at all scales. Mathematical models have allowed our understanding of root and soil interactions to be improved, but are almost invariably reliant on idealised geometries or virtual root growth models. In order to improve phenotyping of advantageous traits for low-P conditions and improve the accuracy of root growth and uptake models, more sophisticated and robust approaches to in vivo root and soil characterisation are needed. Microfocus X-ray Computed Tomography (?-CT) is a methodology that has shown promise for noninvasive imaging of roots and soil at various scales. However, this potential has not been extended to consideration of either very small (rhizosphere scale) or large (mature root system scale) samples. This thesis combines discovery experiments and method development in order to achieve two primary objectives:• The development of more robust, well-described approaches to root and soil ?-CT imaging. Chapters 2 and 3 explore the potential of clinical contrasting methods in root investigation, and show how careful consideration of imaging parameters combined with development of user invariant image-processing protocol can improve measurement of macro-porous volume fraction, a key soil parameter. • Chapter 4 develops an assay for first-time 3D imaging of root hairs in situ within the rhizosphere. The resulting data is used to parameterise an explicit P uptake model at the hair scale, suggesting a different contribution of hairs to uptake than was predicted using idealised geometries. Chapter 5 then extends the paradigm for root hair imaging and model generation, building a robust, modular workflow for investigating P dynamics in the rhizosphere that can accommodate non-optimal soil-water states
Explicit structural modelling of root-hair and soil interactions at the micron-scale parameterized by synchrotron X-ray computed tomography
No full textBackground: the rhizosphere is a zone of fundamental importance for understanding the dynamics of nutrient acquisition by plant roots. The canonical difficulty of experimentally investigating the rhizosphere led long ago to the adoption of mathematical models, the most sophisticated of which now incorporate explicit representations of root hairs and rhizosphere soil. Mathematical upscaling regimes, such as homogenisation, offer the possibility of incorporating into larger scale models the important mechanistic processes occurring at the rhizosphere scale. However, we lack concrete descriptions of all the features required to fully parameterise models at the rhizosphere scale.Scope : by combining Synchrotron X-ray Computed Tomography (SRXCT) and a novel root growth assay, we derive a three-dimensional description of rhizosphere soil structure suitable for use in multi-scale modelling frameworks. We describe an approach to mitigate sub-optimal root-hair detection via structural root-hair growth modelling. The growth model is explicitly parameterized with SRXCT data, and simulates three-dimensional root hair ideotypes in silico, which are suitable for both ideotypic analysis and parameterisation of 3D geometry in mathematical models. Conclusions: the study considers different hypothetical conditions governing root hair interactions with soil matrices, with their respective effects on hair morphology being compared between idealized and image-derived soil/root geometries. The studies in idealised geometries suggest that packing arrangement of soil affects hair tortuosity more than the particle diameter. Results:in field-derived soil suggest that hair access to poorly-mobile nutrients is particularly sensitive to the physical interaction between the growing hairs and the phase of the soil in which soil water is present (i.e. the hydrated textural phase). The general trends in fluid-coincident hair length with distance from the root, and their dependence on hair/soil interaction mechanisms, are conserved across Cartesian and cylindrical geometries.<br/
Poro-elastic Dataset
No full textDataset 01 for: K.R. Daly, S.D. Keyes, and T. Roose, Determination of macro-scale soil properties from pore scale structures - Image based modelling of poroelastic structures, Proc. Roy. Soc. A. 2018 </span
A robust approach for determination of the macro-porous volume fraction of soils with X-ray computed tomography and an image processing protocol
No full textSoil structure is known to govern aspects of hydration, aeration, faunal activity and root growth, which influence plant development. Industrial X-ray computed tomography (?CT) has been used for over 15 years for the elucidation of soil structure, leading to a number of valuable insights. However, there is evidence of a need for more robust, repeatable methods for segmentation of significant structural features, which are essentially free from operator interference. We develop in this paper an automatable approach using a seeded region growth (SRG) algorithm for segmentation of the connected, macroporous domain of homogenized, real soils. Furthermore, we demonstrate methods for user-independent selection of seed point and tolerance values, leading to a fully automated segmentation regime. The stability of this approach to different seed locations has been assessed, as well as the impact of X-ray target and filter choice upon mitigation of artifacts, which are particularly detrimental to accuracy of SRG methods. Estimated porosity derived using this method has been compared with values from a gravimetric protocol and histogram thresholding approaches. It is seen that substantial differences exist in porosity quantified by such methods, with these differences probably the result of varying categorization of different porosity domains
Determination of macro-scale soil properties from pore scale structures: Image based modelling of poroelastic structures
No full textWe show how a combination of X-ray Computed Tomography and image based modelling can be used to calculate the effect of moisture content and compaction on the macroscopic structural properties of soil. Our method is based on the equations derived in [1], which we have extended so they can be directly applied to segmented images obtained from X-ray Computed Tomography. We assume that the soils are composed of air filled pore space, solid mineral grains and a mixed phase composed of both clay particles and water. We considered three different initial soil treatments, comprised of two different compaction levels and two different moisture contents. We found that the effective properties of the soils were unaffected by compaction over the range tested in this paper. However, changing the moisture content significantly altered the hydraulic and mechanical properties of the soils. A key strength of this method is that it enables the optimization,or even design of soils composed from different constituents, with specific mechanical and hydraulic properties
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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