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14 items found (0 items not approved), displaying 1 to 10.[First/Prev] 1, 2 [Next/Last]

Instruments / Technical Area	Publication Details	Published
I13-2-Diamond Manchester Imaging	Comparison of methods to segment variable-contrast XCT images of methane-bearing sand using U-nets trained on single dataset sub-volumes Fernando Alvarez-Borges , Oliver N. F. King , Bangalore N. Madhusudhan , Thomas Connolley , Mark Basham , Sharif I. Ahmed Methane 2, 1 - 23 DOI: 10.3390/methane2010001 Diamond Proposal Number(s): [16205] Open Access Show Abstract ▼ Abstract: Methane (CH4) hydrate dissociation and CH4 release are potential geohazards currently investigated using X-ray computed tomography (XCT). Image segmentation is an important data processing step for this type of research. However, it is often time consuming, computing resource-intensive, operator-dependent, and tailored for each XCT dataset due to differences in greyscale contrast. In this paper, an investigation is carried out using U-Nets, a class of Convolutional Neural Network, to segment synchrotron XCT images of CH4-bearing sand during hydrate formation, and extract porosity and CH4 gas saturation. Three U-Net deployments previously untried for this task are assessed: (1) a bespoke 3D hierarchical method, (2) a 2D multi-label, multi-axis method and (3) RootPainter, a 2D U-Net application with interactive corrections. U-Nets are trained using small, targeted hand-annotated datasets to reduce operator time. It was found that the segmentation accuracy of all three methods surpass mainstream watershed and thresholding techniques. Accuracy slightly reduces in low-contrast data, which affects volume fraction measurements, but errors are small compared with gravimetric methods. Moreover, U-Net models trained on low-contrast images can be used to segment higher-contrast datasets, without further training. This demonstrates model portability, which can expedite the segmentation of large datasets over short timespans.	Dec 2022
DIAD-Dual Imaging and Diffraction Beamline	DIAD: A new instrument for Dual Imaging and Diffraction at Diamond Light Source Sharif Ahmed , Hans Deyhle , Andrew James , James Le Houx , Peter Garland , Michael Drakopoulos , Christina Reinhard , Navid Aslani SPIE Optical Engineering + Applications 2022 DOI: 10.1117/12.2644677 Show Abstract ▼ Abstract: The DIAD beamline at Diamond Light Source is a new dual-beam instrument for quasi-simultaneous full-field imaging and powder diffraction. DIAD enables its users to visualise internal structures (in 2- and 3D) as well as identify and measure compositional and strain changes. The aim is to enable in-situ and in-operando experiments that require spatially correlated results from both X-ray Computed Tomography and X-ray Powder Diffraction. DIAD has two independent beams in the medium energy range (8-38keV) that are generated from a single source 10-pole wiggler. Both beams are combined at one sample position. Here, radiography and/or tomography can be performed using either a monochromatic or pink beam, with a 1.4 mm x 1.2mm field of view and a pixel size of 0.5 µm. Micro-diffraction is possible with a variable beam size between 13µm x 5 µm up to 50 µm x 50µm. The talk will start with a description of the multi-modal capabilities of DIAD and the unique data collection pipeline that has been developed to reduce post-processing workloads. This will be followed by recent results from the fields of material science and bioengineering. Finally, the talk will conclude by giving the audience tips on how to gain access to DIAD.	Oct 2022
DIAD-Dual Imaging and Diffraction Beamline	Flexible positioning of a large area detector using an industrial robot Christina Reinhard , Michael Drakopoulos , Christopher M. Charlesworth , Andrew James , Hiten Patel , Paul Tutthill , Davide Crivelli , Hans Deyhle , Sharif I. Ahmed Journal Of Synchrotron Radiation 29, 1004 - 1013 DOI: 10.1107/S1600577522006300 Diamond Proposal Number(s): [30995] Open Access Show Abstract ▼ Abstract: The DIAD beamline for Dual Imaging and Diffraction at Diamond Light Source has opted to use an industrial robot to position its Dectris Pilatus 2M CdTe diffraction detector. This setup was chosen to enable flexible positioning of the detector in a quarter-sphere around the sample position whilst reliably holding the large weight of 139 kg of detector, detector mount and cabling in a stable position. Metrology measurements showed that the detector can be positioned with a linear repeatability of <19.7 µm and a rotational repeatability of <16.3 µrad. The detector position stays stable for a 12 h period with <10.1 µm of movement for linear displacement and <3.8 µrad for rotational displacement. X-ray diffraction from calibration samples confirmed that the robot is sufficiently stable to resolve lattice d-spacings within the instrumental broadening given by detector position and beam divergence.	Jul 2022
I12-JEEP: Joint Engineering, Environmental and Processing	Correlative neutron and X-ray tomography imaging of pile installation in chalk Fernando Alvarez-Borges , Genoveva Burca , Robert Atwood , Andrew James , Mark Wolstenholme , Sharif Ahmed Géotechnique DOI: 10.1680/jgeot.21.00318 Diamond Proposal Number(s): [26232] Show Abstract ▼ Abstract: Neutron and X-ray tomography (NCT and XCT, respectively) are imaging techniques increasingly being applied in geomechanics research. They are used to non-destructively reveal different microstructural aspects of geomaterials: XCT is often used to observe/quantify differences in density or porosity, while NCT reveals the presence and distribution of hydrogenous materials such as water. The correlated use of NCT and XCT for geomechanics and geotechnics research is in its infancy. To this date, very few experiments have been carried out that combine both techniques, and none have been used to investigate geomaterial-structure interaction. This paper presents the first correlative NCT-XCT imaging study of pile installation. A scaled model pile was installed in an unsaturated intact chalk cylinder and in-situ NCT and ex-situ XCT synchrotron-based imaging was applied consecutively. Chalk was used because the behaviour of displacement piles installed in this material is still subject to considerable uncertainty. Results reveal for the first time the interaction between installation-induced changes in chalk density and water distribution variations, with evidence of water displacement into the densified material in the vicinity of the installed pile. A straightforward method for correlative bulk density-moisture content determination from NCT-XCT images of geomaterials are presented and their limitations discussed.	Jul 2022
I13-2-Diamond Manchester Imaging	Gas bubble dynamics during methane hydrate formation and its influence on geophysical properties of sediment using high-resolution synchrotron imaging and rock physics modeling B. N. Madhusudhan , S. K. Sahoo , F. Alvarez-Borges , S. Ahmed , L. J. North , A. I. Best Frontiers In Earth Science 10 DOI: 10.3389/feart.2022.877641 Diamond Proposal Number(s): [16205] Open Access Show Abstract ▼ Abstract: Gas bubble in aquatic sediments has a significant effect on its geophysical and geomechanical properties. Recent studies have shown that methane gas and hydrate can coexist in gas hydrate–bearing sediments. Accurate calibration and understanding of the fundamental processes regarding such coexisting gas bubble dynamics is essential for geophysical characterization and hazard mitigation. We conducted high-resolution synchrotron imaging of methane hydrate formation from methane gas in water-saturated sand. While previous hydrate synchrotron imaging has focused on hydrate evolution, here we focus on the gas bubble dynamics. We used a novel semantic segmentation technique based on convolutional neural networks to observe bubble dynamics before and during hydrate formation. Our results show that bubbles change shape and size even before hydrate formation. Hydrate forms on the outer surface of the bubbles, leading to reduction in bubble size, connectivity of bubbles, and the development of nano-to micro-sized bubbles. Interestingly, methane gas bubble size does not monotonously decrease with hydrate formation; rather, we observe some bubbles being completely used up during hydrate formation, while bubbles originate from hydrates in other parts. This indicates the dynamic nature of gas and hydrate formation. We also used an effective medium model including gas bubble resonance effects to study how these bubble sizes affect the geophysical properties. Gas bubble resonance modeling for field or experimental data generally considers an average or equivalent bubble size. We use synchrotron imaging data to extract individual gas bubble volumes and equivalent spherical radii from the segmented images and implement this into the rock physics model. Our modeling results show that using actual bubble size distribution has a different effect on the geophysical properties compared to the using mean and median bubble size distributions. Our imaging and modeling studies show that the existence of these small gas bubbles of a specific size range, compared to a bigger bubble of equivalent volume, may give rise to significant uncertainties in the geophysical inversion of gas quantification.	Jun 2022
I12-JEEP: Joint Engineering, Environmental and Processing	On acquisition parameters and processing techniques for interparticle contact detection in granular packings using synchrotron computed tomography Fernando Alvarez-Borges , Sharif Ahmed , Robert C. Atwood Journal Of Imaging 8 DOI: 10.3390/jimaging8050135 Diamond Proposal Number(s): [26307] Open Access Show Abstract ▼ Abstract: X-ray computed tomography (XCT) is regularly employed in geomechanics to non-destructively measure the solid and pore fractions of soil and rock from reconstructed 3D images. With the increasing availability of high-resolution XCT imaging systems, researchers now seek to measure microfabric parameters such as the number and area of interparticle contacts, which can then be used to inform soil behaviour modelling techniques. However, recent research has evidenced that conventional image processing methods consistently overestimate the number and area of interparticle contacts, mainly due to acquisition-driven image artefacts. The present study seeks to address this issue by systematically assessing the role of XCT acquisition parameters in the accurate detection of interparticle contacts. To this end, synchrotron XCT has been applied to a hexagonal close-packed arrangement of glass pellets with and without a prescribed separation between lattice layers. Different values for the number of projections, exposure time, and rotation range have been evaluated. Conventional global grey value thresholding and novel U-Net segmentation methods have been assessed, followed by local refinements at the presumptive contacts, as per recently proposed contact detection routines. The effect of the different acquisition set-ups and segmentation techniques on contact detection performance is presented and discussed, and optimised workflows are proposed.	May 2022
DIAD-Dual Imaging and Diffraction Beamline	Beamline K11 DIAD: a new instrument for dual imaging and diffraction at Diamond Light Source Christina Reinhard , Michael Drakopoulos , Sharif I. Ahmed , Hans Deyhle , Andrew James , Christopher M. Charlesworth , Martin Burt , John Sutter , Steven Alexander , Peter Garland , Thomas Yates , Russell Marshall , Ben Kemp , Edmund Warrick , Armando Pueyos , Ben Bradnick , Maurizio Nagni , A. Douglas Winter , Jacob Filik , Mark Basham , Nicola Wadeson , Oliver N. F. King , Navid Aslani , Andrew J. Dent Journal Of Synchrotron Radiation 28 DOI: 10.1107/S1600577521009875 Open Access Show Abstract ▼ Abstract: The Dual Imaging and Diffraction (DIAD) beamline at Diamond Light Source is a new dual-beam instrument for full-field imaging/tomography and powder diffraction. This instrument provides the user community with the capability to dynamically image 2D and 3D complex structures and perform phase identification and/or strain mapping using micro-diffraction. The aim is to enable in situ and in operando experiments that require spatially correlated results from both techniques, by providing measurements from the same specimen location quasi-simultaneously. Using an unusual optical layout, DIAD has two independent beams originating from one source that operate in the medium energy range (7–38 keV) and are combined at one sample position. Here, either radiography or tomography can be performed using monochromatic or pink beam, with a 1.4 mm × 1.2 mm field of view and a feature resolution of 1.2 µm. Micro-diffraction is possible with a variable beam size between 13 µm × 4 µm and 50 µm × 50 µm. One key functionality of the beamline is image-guided diffraction, a setup in which the micro-diffraction beam can be scanned over the complete area of the imaging field-of-view. This moving beam setup enables the collection of location-specific information about the phase composition and/or strains at any given position within the image/tomography field of view. The dual beam design allows fast switching between imaging and diffraction mode without the need of complicated and time-consuming mode switches. Real-time selection of areas of interest for diffraction measurements as well as the simultaneous collection of both imaging and diffraction data of (irreversible) in situ and in operando experiments are possible.	Nov 2021
	Investigation of pile penetration in calcareous soft rock using X-ray computed tomography Fernando Alvarez-Borges , Sharif Ahmed , Bangalore Narasimha Madhusudhan , David Richards International Journal Of Physical Modelling In Geotechnics DOI: 10.1680/jphmg.20.00031 Open Access Show Abstract ▼ Abstract: Penetration of open- and closed-ended model piles into intact chalk, a soft calcareous rock, was investigated using microfocus X-ray computed tomography (XCT). 3D images of the specimens showed that the piles crushed and densified the chalk in their path, creating a crushed chalk annulus around the shaft, a region of compressed destructured chalk below the tip, and fractures across cemented regions of the specimen. Laser-diffraction particle size analyses of the crushed chalk annulus after exhumation showed limited difference with laboratory-remoulded chalk, which suggested thorough de-cementation. Installation stresses and XCT-derived densities were paired using a simplified cylindrical cavity expansion solution to estimate effective radial stress-void ratio states at the pile tip during penetration. More complex numerical solutions could not be applied using the available data. This approach posed significant problems, as it could not suitably incorporate hardening and non-linear stiffness behaviours of Chalk during pile penetration, nor account for the creation of discontinuities. However, effective radial stress-void ratio estimates were found to converge with the reconstituted critical state line of the material at high stresses and low void ratios. This partially supported the use of a critical state framework to characterise pile penetration in Chalk, as proposed in recent literature.	Nov 2020
I13-2-Diamond Manchester Imaging	Optimal X-ray micro-CT image based methods for porosity and permeability quantification in heterogeneous sandstones Ben Callow , Ismael Falcon-Suarez , Hector Marin-Moreno , Jonathan M. Bull , Sharif Ahmed Geophysical Journal International DOI: 10.1093/gji/ggaa321 Diamond Proposal Number(s): [18758] Show Abstract ▼ Abstract: 3D X-ray micro-CT (XCT) is a non-destructive 3D imaging method, increasingly used for a wide range of applications in Earth Science. An optimal XCT image-processing workflow is derived here for accurate quantification of porosity and absolute permeability of heterogeneous sandstone samples using an assessment of key image acquisition and processing parameters: Image resolution, segmentation method, representative elementary volume (REV) size and fluid-simulation method. XCT image-based calculations obtained for heterogeneous sandstones are compared to two homogeneous standards (Berea sandstone and a sphere pack), as well as to the results from physical laboratory measurements. An optimal XCT methodology obtains porosity and permeability results within ± 2 per cent and vary by one order of magnitude around the direct physical measurements, respectively, achieved by incorporating the clay fraction and cement matrix (porous, impermeable components) to the pore-phase for porosity calculations and into the solid-phase for permeability calculations. Two Stokes-flow finite element modelling (FEM) simulation methods, using a voxelised grid (Avizo) and tetrahedral mesh (Comsol) produce comparable results, and similarly show that a lower resolution scan (∼5 µm) is unable to resolve the smallest intergranular pores, causing an underestimation of porosity by ∼3.5 per cent. Downsampling the image-resolution post-segmentation (numerical coarsening) and pore network modelling both allow achieving of a representative elementary volume (REV) size, whilst significantly reducing fluid simulation memory requirements. For the heterogeneous sandstones, REV size for permeability (≥ 1 cubic mm) is larger than for porosity (≥ 0.5 cubic mm) due to tortuosity of the fluid paths. This highlights that porosity should not be used as a reference REV for permeability calculations. The findings suggest that distinct image processing workflows for porosity and permeability would significantly enhance the accurate quantification of the two properties from XCT.	Jun 2020
	X-ray computed tomography reveals that grain protrusion controls critical shear stress for entrainment of fluvial gravels Rebecca A. Hodge , Hal Voepel , Julian Leyland , David A. Sear , Sharif Ahmed Geology 48, 149 - 153 DOI: 10.1130/G46883.1 Open Access Show Abstract ▼ Abstract: The critical shear stress (τc) for grain entrainment is a poorly constrained control on bedload transport rates in rivers. Direct calculations of τc have been hindered by the inability to measure the geometry of in situ grains; i.e., the shape and location of each grain relative to surrounding grains and the bed surface. We present the first complete suite of three-dimensional (3-D) grain geometry parameters for 1055 water-worked grains, and use these to parameterize a new 3-D grain entrainment model and hence estimate τc. The 3-D data were collected using X-ray computed tomography scanning of sediment samples extracted from a prototype scale flume experiment. We find that (1) parameters including pivot angle and proportional grain exposure do not vary systematically with relative grain size; (2) τc is primarily controlled by grain protrusion, not pivot angle; and (3) larger grains experience larger forces as a result of projecting higher into the flow profile, producing equal mobility. We suggest that grain protrusion is a suitable proxy for assessing gravel-bed stability.	Nov 2019

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