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Regular physical activity (PA) is known to reduce the risk of serious community-acquired infections. We examined the association of PA with the morbidity and mortality resulting from coronavirus disease (COVID-19) infection in the South Korean population. Patients who tested positive for severe acute respiratory coronavirus 2 and who underwent public health screening between 2014 and 2017 (n = 6288) were included. Age- and sex-matched controls (n = 125,772) were randomly selected from the Korean National Health Insurance Service database. Leisure-time PA was assessed using a self-reported questionnaire. The mean PA levels were lower in the patient than in the control group (558.2 ± 516.3 vs. 580.2 ± 525.7 metabolic equivalent of task (MET)-min/week, p = 0.001). Patients with moderate to vigorous PA (MVPA) were associated with a lower risk of COVID-19 morbidity (odds ratio (OR), 0.90; 95% confidence interval (CI), 0.86–0.95). In addition, a standard deviation (SD) increment in MET/week (525.3 MET-min/week) was associated with a 4% decrease in the risk of COVID-19 morbidity (OR, 0.96; 95% CI, 0.93–0.99). MVPA and an SD increment in MET/week were associated with lower mortality (MVPA: OR, 0.47; 95% CI, 0.26–0.87; per SD increment: OR, 0.65; 95% CI, 0.48–0.88). Higher levels of regular PA were associated with a lower risk of COVID-19 infection and mortality, highlighting the importance of maintaining appropriate levels of PA along with social distancing amid the COVID-19 pandemic.

Hydraulic stimulation has been a key technique in enhanced geothermal systems (EGS) and the recovery of unconventional hydrocarbon resources to artificially generate fractures in a rock formation. Previous experimental studies present that the pattern and aperture of generated fractures vary as the fracking pressure propagation. The recent development of three-dimensional X-ray computed tomography allows visualizing the fractures for further analysing the morphological features of fractures. However, the generated fracture consists of a few pixels (e.g., 1-3 pixels) so that the accurate and quantitative extract of micro-fracture is highly challenging. Also, the high-frequency noise around the fracture and the weak contrast across the fracture makes the application of conventional segmentation methods limited. In this study, we adopted an encoder-decoder network with a convolutional neural network (CNN) based on deep learning method for the fast and precise detection of micro-fractures. The conventional image processing methods fail to extract the continuous fractures and overestimate the fracture thickness and aperture values while the CNN-based approach successfully detects the barely seen fractures. The reconstruction of the 3D fracture surface and quantitative roughness analysis of fracture surfaces extracted by different methods enables comparison of sensitivity (or robustness) to noise between each method.

Liquid CO2 fracturing is a promising alternative to hydraulic fracturing since it can circumvent problems stemming from the use of water. One of the most significant differences between liquid CO2 and hydraulic fracturing processes is that liquid CO2 permeates into matrix pores very rapidly due to its low viscosity. Here we study how this rapid permeation of liquid CO2 impacts a range of features during the course of the fracturing process, with a focus on the breakdown pressure and cracking behavior. We first conduct a series of laboratory fracturing experiments that inject liquid CO2, water, and oil into nominally identical mortar specimens with various pressurization rates. We quantitatively measure the volumes of fluids permeated into the specimens and investigate how these permeated volumes are related to breakdown and fracture initiation pressures and pressurization efficiency. The morphology of the fractures generated by different types of fluids is also examined using 3D X-ray computed tomographic imaging. Subsequently, the cracking processes due to injection of liquid CO2 and water are further investigated by numerical simulations employing a phase-field approach to fracture in porous media. Simulation results show that rapid permeation of liquid CO2 gives rise to a substantial pore pressure buildup and distributed microcracks prior to the major fracture propagation stage. The experimental and numerical results commonly indicate that significant fluid permeation during liquid CO2 fracturing is a primary reason for its lower breakdown pressure and more distributed fractures compared with hydraulic fracturing.

U–Zr–RE heel residue was manufactured after fabricating U–Zr–RE fuel slugs by an injection casting method. In order to increase the fabrication yield rate, the uranium scrap waste should be reused as raw materials through surface treatment. Various impurity elements existed on the surface of the heel residue. Scanning electron microscopy and Energy-dispersive X-ray spectroscopy results showed that rare-earth elements in the dilute nitric acid were removed using air agitation. Impurity elements for the heel residue were removed from the top and bottom layers by pickling. Metallic fuel slugs were soundly fabricated using the pickled heel residue as raw materials.

Hydraulic fracturing by liquid carbon dioxide (LCO 2 ) generates fracture and cracking patterns that vary from those generated by water injection . The use of LCO 2 as a fracturing fluid can minimize water usage and potentially sequester CO2. In this study, hydraulic fracturing by LCO2 and water in a granitic specimen was performed, and the micro-scale characteristics of generated microcracks were investigated using an X-ray imaging technique and thin-section analysis. The results revealed that LCO 2 and water injection produced different fracture characteristics . The injection of LCO 2 with less viscosity and high compressibility required a greater fluid volume for fracture initiation to generate a lower breakdown pressure , and also generated higher crack-density zones located near the borehole hole possibly because of facilitated permeation amount into the rock matrix as compared to the water-injection case. In both the LCO 2 - and water-injection cases, the fractures developed along the rift cleavage plane, and an increase in microcrack density was observed in regions within 6 mm from the borehole. It was confirmed that the statistical and spatial distributions of developed microcracks were affected by the fracturing fluid and anisotropic properties of granitic rocks. The results of this study could be applied to fracturing that employs less water, CO 2 sequestration, and recovery of geothermal energy .

This study investigated carbon contamination in U-10wt.%Zr metallic fuel in the casting process based on the interaction between the U-Zr alloy melt and the Y2O3-plasma-spray-coated graphite. During the injection casting of U-10wt.%Zr, a ZrC reaction layer was found to form at the interface between the U-Zr melt and the Y2O3-plasma-coated graphite crucible. ZrC inclusions were also found in the matrix of the melt residue. This C contamination, evidenced by the formation of ZrC, is attributed to the migration of C through the Y2O3 coating from the graphite crucible. The results of TGA experiments using a Y2O3-plasma-coated graphite sample suggest that CO is produced by a reaction between Y2O3 and graphite at temperatures above 1773 K, which then migrates through defects in the coating to react with Zr in the U-Zr melt.

The remote injection casting process was developed using a high-capacity casting system in a mockup facility to secure the key technology for the fabrication of transmutation metallic fuels in hot cells. Seventy-eight fuel slugs fabricated simultaneously through remote injection casting were confirmed to satisfy the fabrication specification. The reaction characteristics of the coating candidates for the reusable crucible were investigated by using sessile drop tests with U-10wt%Zr-5wt%RE at 1450 °C for 1 h and LaYO3 showed the smallest interaction width. The improvement in the adhesion of Y2O3 coatings on the inner walls of the quartz mold was effective in reducing the reaction between the melt and the mold. The mechanical and chemical cleaning processes were investigated to remove the surface contamination layer of the melt residue for recycling. Both cleaning methods were effective with the mechanical treatment favored owing to the operations in hot cells. The remote injection casting process equipped with fuel loss control components developed in this work will fabricate transmutation fuels in hot cells.

The sizes of microstructural features determine the mechanical behaviors of rocks, but the complex nature of their structures frequently hinders the precise quantification of the feature sizes. This study presents a digital-image-based quantification for evaluating the representative sizes of the microstructures in rocks. This method, using a madogram function, allows obtaining a single length value that uniquely represents the internal scales of the constituents in a heterogeneous material based on 3D X-ray computed tomographic images. The madogram function has the advantage of being applicable to grayscale images without any post-processing, which overcomes the limited applicability of previous correlation methods. The method was first validated in patterned and random heterogeneous domains that were synthetically prepared. Then, we further validated the method using original 16-bit μ-CT images of 14 rock samples with the consideration of domain size and image resolution. The measurements of the geophysical properties were performed to investigate their correlation with the representative sizes of the microstructures in rocks.

For the mitigation of micro-seismicity during hydraulic stimulation, we introduce the concept of time-delayed pressurization (TDP) which involves arresting the constant-rate process of borehole pressurization for a given delay period, and then resuming it until breakdown occurs. The additional fluid permeation into a porous media by the TDP scheme allows for the manipulation of pore fluid pressure buildup near a borehole, thereby resulting in the mechanical and seismic behaviors at failure in a controlled manner. Laboratory fracturing experiments with acoustic emission monitoring were conducted for several delay periods using mortar specimens to evaluate the breakdown pressure and acoustic emission (AE) in the TDP fracturing process. In addition, the morphological characteristics of induced fractures were visually investigated by 3D X-ray CT analysis on the fractured specimens. Numerical simulations using a phase-field approach were also performed to further examine the evolution of pore pressure during the fracturing process. The results show the considerable volume of permeated fluid and the elevated pore pressure during the delay period are the main factors responsible for the decreased breakdown pressure and AE.