Water refilling along vessels at initial stage of willow cuttage revealed by move contrast CT

Cuttage is a widely used technique for plant propagation, whose success relies on the refilling for water transport recovery. However, requirements for refilling characterization studies, including large penetration depth, fast temporal resolution and high spatial resolution, cannot be reached simultaneously via conventional imaging techniques. So far, the dynamic process of water refilling along the vessels at the initial stage of cuttage, as well as its characteristics, remains unclear. Hereby, we developed a move contrast X-ray microtomography method which achieves 3D dynamic non-destructive imaging of water refilling at the initial stage of willow branch cuttage, without the aid of any contrast agent. Experimental results indicate three primary refilling modalities in vessels: 1) the osmosis type, mainly manifested by the osmosis of tissue through the vessel wall into the cavity; 2) the linear type, revealed as the tissue permeates to a certain extent where the liquid column in the vessels is completely formed; and 3) an osmosis-linear mixed type refilling as an intermediate state. Further analysis also exhibits a “temporal-spatial relay” mode of refilling between adjacent vessels. Since the vessel length is quite limited, the cavitation and the relay refilling mode of vessels can be an important way to achieve long-distance water transport

Phase retrieval in quantitative x-ray microtomography with a single sample-to-detector distance

Phase retrieval extracts quantitative phase information from x-ray propagation-based phase-contrast images. Notwithstanding inherent approximations, phase retrieval using a single sample-to-detector distance (SDD) is very attractive, because it imposes no setup complications or additional radiation dose compared to absorption-based imaging. Considering the phase-attenuation duality (ε =δ/β, where ε is constant), a simple absorption correction factor is proposed for the modified Bronnikov algorithm in x-ray propagation-based phase-contrast computed tomography (PPCT). Moreover, a practical method for calculating the optimal ε value is proposed, which requires no prior knowledge of the sample. Tests performed on simulation and experimental data successfully distinguished different materials in a quasihomogeneous and weakly absorbing sample from a single SDD-PPCT data point

Origin of Non-cubic Scaling Law in Disordered Granular Packing

Recent diffraction experiments on metallic glasses have unveiled an unexpected non-cubic scaling law between density and average interatomic distance, which lead to the speculations on the presence of fractal glass order. Using X-ray tomography we identify here a similar non-cubic scaling law in disordered granular packing of spherical particles. We find that the scaling law is directly related to the contact neighbors within first nearest neighbor shell, and therefore is closely connected to the phenomenon of jamming. The seemingly universal scaling exponent around 2.5 arises due to the isostatic condition with contact number around 6, and we argue that the exponent should not be universal.Comment: 24 pages, 8 figures,to be published in Phys. Rev. Let

Structural and Topological Nature of Plasticity in Sheared Granular Materials

Upon mechanical loading, granular materials yield and undergo plastic deformation. The nature of plastic deformation is essential for the development of the macroscopic constitutive models and the understanding of shear band formation. However, we still do not fully understand the microscopic nature of plastic deformation in disordered granular materials. Here we used synchrotron X-ray tomography technique to track the structural evolutions of three-dimensional granular materials under shear. We establish that highly distorted coplanar tetrahedra are the structural defects responsible for microscopic plasticity in disordered granular packings. The elementary plastic events occur through flip events which correspond to a neighbor switching process among these coplanar tetrahedra (or equivalently as the rotation motion of 4-ring disclinations). These events are discrete in space and possess specific orientations with the principal stress direction.Comment: 26 pages, 11 figures, 2 tables, to be published in Nature Communication

Fast and accurate X-ray fluorescence computed tomography imaging with the ordered-subsets expectation maximization algorithm.

The ordered-subsets expectation maximization algorithm (OSEM) is introduced to X-ray fluorescence computed tomography (XFCT) and studied; here, simulations and experimental results are presented. The simulation results indicate that OSEM is more accurate than the filtered back-projection algorithm, and it can efficiently suppress the deterioration of image quality within a large range of angular sampling intervals. Experimental results of both an artificial phantom and cirrhotic liver show that with a satisfying image quality the angular sampling interval could be improved to save on the data-acquisition time when OSEM is employed. In addition, with an optimum number of subsets, the image reconstruction time of OSEM could be reduced to about half of the time required for one subset. Accordingly, it can be concluded that OSEM is a potential method for fast and accurate XFCT imaging

Ultrafast Radiographic Imaging and Tracking: An overview of instruments, methods, data, and applications

Ultrafast radiographic imaging and tracking (U-RadIT) use state-of-the-art ionizing particle and light sources to experimentally study sub-nanosecond dynamic processes in physics, chemistry, biology, geology, materials science and other fields. These processes, fundamental to nuclear fusion energy, advanced manufacturing, green transportation and others, often involve one mole or more atoms, and thus are challenging to compute by using the first principles of quantum physics or other forward models. One of the central problems in U-RadIT is to optimize information yield through, e.g. high-luminosity X-ray and particle sources, efficient imaging and tracking detectors, novel methods to collect data, and large-bandwidth online and offline data processing, regulated by the underlying physics, statistics, and computing power. We review and highlight recent progress in: a.) Detectors; b.) U-RadIT modalities; c.) Data and algorithms; and d.) Applications. Hardware-centric approaches to U-RadIT optimization are constrained by detector material properties, low signal-to-noise ratio, high cost and long development cycles of critical hardware components such as ASICs. Interpretation of experimental data, including comparisons with forward models, is frequently hindered by sparse measurements, model and measurement uncertainties, and noise. Alternatively, U-RadIT makes increasing use of data science and machine learning algorithms, including experimental implementations of compressed sensing. Machine learning and artificial intelligence approaches, refined by physics and materials information, may also contribute significantly to data interpretation, uncertainty quantification and U-RadIT optimization.Comment: 51 pages, 31 figures; Overview of ultrafast radiographic imaging and tracking as a part of ULITIMA 2023 conference, Mar. 13-16,2023, Menlo Park, CA, US

Study of 20 Hz high spatial-temporal resolution monochromatic X-ray dynamic micro-CT

BackgroundDynamic micro-computed tomography (micro-CT) using monochromatic X-ray offers higher density resolution and lower radiation damage compared to that using white X-ray, however balancing its imaging spatial and temporal resolution is challenging. Currently, the reported highest temporal resolution of monochromatic X-ray dynamic micro-CT is 13.3 Hz with a detector effective pixel size of 5 μm.PurposeThis study aims to develop a monochromatic X-ray dynamic micro-CT system with a higher spatial and temporal resolution to meet the experimental needs of the fast X-ray imaging beamline (BL16U2) users at Shanghai Synchrotron Radiation Facility (SSRF).MethodsFirstly, an experimental system of dynamic micro-CT with the high flux density monochromatic X-ray from an undulator source was established by combination of a high-speed rotary stage and a large numerical aperture triple-lens fast X-ray imaging detection system on the BL16U2 beamline at SSRF. Then, a demonstration experiment with a fast-foaming polyurethane material as a sample was performed to examine the spatial-temporal resolution of this experimental system, moreover a quantitative analysis of the bubble motion during foaming process was performed.ResultsExperimental results of foaming process of the fast-foaming polyurethane material based on the monochromatic X-ray dynamic micro-CT system show that a temporal resolution of 20 Hz of the dynamic micro-CT was achieved with 15 keV monochromatic X-ray and an effective detector pixel size of 2.2 μm.ConclusionsThe developed monochromatic X-ray dynamic micro-CT system has a high spatial-temporal resolution and can perform four-dimensional quantitative analysis of complex motion systems, providing a powerful experimental research platform for users of BL16U2 beamline at SSRF