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Vegetation on railway or highway slopes can improve slope stability through the generation of soil pore water suctions by plant transpiration and mechanical soil reinforcement by the roots. To incorporate the enhanced shearing resistance and stiffness of root-reinforced soils in stability calculations, it is necessary to understand and quantify its effectiveness. This requires integrated and sophisticated experimental and multi-scale modelling approaches to develop an understanding of the processes at different length scales, from individual root–soil interaction through to full soil-profile or slope scale. One of the challenges with multi-scale models is ensuring that they sufficiently closely represent real behaviour. This requires calibration against detailed high-quality and data-rich experiments. This study presents a novel experimental methodology, which combines in situ direct shear loading of a willow root-reinforced soil with X-ray computed tomography to capture the three-dimensional chronology of soil and root deformation within the shear zone. Digital volume correlation (DVC) analysis was applied to the computed tomography dataset to obtain full-field three-dimensional displacement and strain information. This paper demonstrates the feasibility and discusses the challenges associated with DVC experiments on root-reinforced soils. [ABSTRACT FROM AUTHOR]

We show how a combination of X-ray computed tomography (X-CT) 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 Daly & Roose (2018 Proc. R. Soc. A 474, 20170141. (doi:10.1098/rspa.2017.0141)), which we have extended so they can be directly applied to the segmented images obtained from X-CT. 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, composed of two different compaction levels and two differentmoisture 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. [ABSTRACT FROM AUTHOR]

Muscle spindles are skeletal muscle sensory organs involved in the sensation of position and movement of the body. We have explored the capability of phase contrast computed tomography to visualise muscle spindles in murine skeletal muscle. In particular, we have validated the visualisation of nerve fibres through phase contrast computed tomography using light microscopy on stained histological sections. We further present the first three-dimensional visualisation of muscle spindles in mouse soleus skeletal muscle in conjunction with the neurovascular bundle associated with it. [ABSTRACT FROM AUTHOR]

Conventional models of solute transport in soil consider only soil volumes large enough to average over microscale heterogeneities, and it is assumed that microscale variations are unimportant at the macroscale. In this research we test this assumption for cases in which the microscale distribution of solute-sorbing sites is patchy. We obtain a set of equations at the macroscale that allow for the effect of the microscale distribution with the mathematical technique of homogenization. We combine these equations with an image-based model that describes the true microscale pore geometry in a real, structured soil measured with X-ray computed tomography. The resulting models are used to test the microscale averaging assumptions inherent in conventional models. We show that, in general, macroscale diffusion is little affected by microscale variation in the distribution of sorption sites. Therefore, for most purposes the assumption of microscale averaging used in conventional models is justified. The effects of microscale heterogeneity are noticeable only when (i) the rate of sorption is slow compared with diffusion, but still fast enough to affect macroscale transport and (ii) the defined macroscale volume approaches the microscale. We discuss the effects when these conditions are met. Highlights When does microscale variation need to be allowed for in macroscale transport and reaction models?, We use image-based modelling and homogenization to answer this., We find macroscale transport is generally little affected by microscale patchiness of sorption sites., The microscale averaging implicit in conventional models is justified in most cases. [ABSTRACT FROM AUTHOR]

Soil structure is known to govern aspects of hydration, aeration, faunal activity and root growth, which influence plant development. Industrial X-ray computed tomography ( μCT) 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. [ABSTRACT FROM AUTHOR]

Flow in both saturated and non-saturated vuggy porous media, i.e. soil, is inherently multiscale. The complex microporous structure of the soil aggregates and the wider vugs provides a multitude of flow pathways and has received significant attention from the X-ray computed tomography (CT) community with a constant drive to image at higher resolution. Using multiscale homogenization, we derive averaged equations to study the effects of the microscale structure on the macroscopic flow. The averaged model captures the underlying geometry through a series of cell problems and is verified through direct comparison to numerical simulations of the full structure. These methods offer significant reductions in computation time and allow us to perform three-dimensional calculations with complex geometries on a desktop PC. The results show that the surface roughness of the aggregate has a significantly greater effect on the flow than the microstructure within the aggregate. Hence, this is the region in which the resolution of X-ray CT for image-based modelling has the greatest impact. [ABSTRACT FROM AUTHOR]

Global food production depends on the application of phosphorus (P) fertilisers, usually sourced from rock phosphate, a non-renewable resource. Optimising P use to ensure sustainable P application is necessary to supply food worldwide and to protect the environment from P runoff. However, standard models used to guide P application on fields are limited due to assumptions that fail to consider the short-term dynamics of P in the soil solution. This study combined time-resolved microdialysis sampling with 4D spatial information from X-ray computed tomography to inform an image-based model for assessing P-soil-plant interactions over the start of a growing season. The time-resolved microdialysis measurements revealed that P released from the granules is rapidly removed from the soil solution in the short-term. We demonstrate that the standard equilibrium models typically used to characterise P transport in soil are not representative of the experimental system on the time scales considered. Instead, an Absorption-Diffusion model, where a single sink term accounts for all the processes removing P from the soil solution was required to correctly characterise experimental observations. Our study provides the basis for a model which could be adapted to predict within-season fertilisation scenarios in different soil conditions, and provides a conceptual description of plant/crop yield response to P fertilisation. [Display omitted] • Phosphorus fertiliser dynamics and inefficiency sources are poorly understood. • We investigated spatiotemporal dynamics of P in soil and plant uptake. • We combined microdialysis, X-ray Computed Tomography and image-based modelling. • Explaining rapid P adsorption in P-poor soil required a novel modelling approach. • New models predict P application is effective in a narrow window of P-soil content. [ABSTRACT FROM AUTHOR]

Lymph nodes are an important part of the immune system. They filter the lymphatic fluid as it is transported from the tissues before being returned to the blood stream. The fluid flow through the nodes influences the behaviour of the immune cells that gather within the nodes and the structure of the node itself. Measuring the fluid flow in lymph nodes experimentally is challenging due to their small size and fragility. In this paper, we present high resolution X-ray computed tomography images of a murine lymph node. The impact of the resulting visualized structures on fluid transport are investigated using an image based model. The high contrast between different structures within the lymph node provided by phase contrast X-ray computed tomography reconstruction results in images that, when related to the permeability of the lymph node tissue, suggest an increased fluid velocity through the interstitial channels in the lymph node tissue. Fluid taking a direct path from the afferent to the efferent lymphatic vessel, through the centre of the node, moved faster than the fluid that flowed around the periphery of the lymph node. This is a possible mechanism for particles being moved into the cortex. [ABSTRACT FROM AUTHOR]

The mechanical impedance of soils inhibits the growth of plant roots, often being the most significant physical limitation to root system development. Non-invasive imaging techniques have recently been used to investigate the development of root system architecture over time, but the relationship with soil deformation is usually neglected. Correlative mapping approaches parameterised using 2D and 3D image data have recently gained prominence for quantifying physical deformation in composite materials including fibre-reinforced polymers and trabecular bone. Digital Image Correlation (DIC) and Digital Volume Correlation (DVC) are computational techniques which use the inherent material texture of surfaces and volumes, captured using imaging techniques, to map full-field deformation components in samples during physical loading. Here we develop an experimental assay and methodology for four-dimensional, in vivo X-ray Computed Tomography (XCT) and apply a Digital Volume Correlation (DVC) approach to the data to quantify deformation. The method is validated for a field-derived soil under conditions of uniaxial compression, and a calibration study is used to quantify thresholds of displacement and strain measurement. The validated and calibrated approach is then demonstrated for an in vivo test case in which an extending maize root in field-derived soil was imaged hourly using XCT over a growth period of 19 h. This allowed full-field soil deformation data and 3D root tip dynamics to be quantified in parallel for the first time. This fusion of methods paves the way for comparative studies of contrasting soils and plant genotypes, improving our understanding of the fundamental mechanical processes which influence root system development. [ABSTRACT FROM AUTHOR]