Study of the slippage of particle / supercritical CO2 two-phase flow

In this paper, the slippage velocity and displacement between particles and supercritical CO2 (SC-CO2) were studied to reveal the particle-SC-CO2 two-phase flow behavior. Visualization experiments were performed to directly measure the slippage velocity and displacement. Eight groups of experiments involving various pressures (7.89–10.96 MPa), temperatures (38.6–47.5 °C), particle diameters (0.3–0.85 mm), particle densities (2630 and 3120 kg/m3) and SC-CO2 flow rates (0.920–1.284 m/s) were conducted. The measured particle slippage velocities in the flowing direction were approximately 10.3% of the SC-CO2 flow rate. The measured particle slippage displacements were all at the centimeter level, which indicated that SC-CO2 had a superior particle transporting capability that was similar to those of liquids even if it had a low viscosity that was similar to those of gases. A numerical model was built, and analytic slippage calculations were performed for SC-CO2 for additional analyses. The density of SC-CO2 was found to have a greater influence on the slippage than the viscosity. Moreover, a comparison of the slippage between SC-CO2 and water showed that the particle slippage in water was constant, while the particle slippage in SC-CO2 continually accumulated at an extremely slow rate

Vegetation growth promotion and overall strength improvement using biopolymers in vegetated soils

Planting vegetation is a sustainable and eco-friendly method for shallow slope stabilization. However, in water-limited regions, this method is facing challenges like retarded vegetation growth, which leads to unprotected soils. Biopolymer, with potentials in both vegetation growth promotion and soil strength enhancement, is therefore tested in this paper with regard to its possibility in assisting soil reinforcement with vegetation through vegetation cultivation and direct shear tests. Both sugar-based and protein-based biopolymers improved water availability to growing plants and nutrient uptake. The most suitable polysaccharide xanthan gum was adopted to further explore the effects of treatment condition (i.e., blending content) and external environment (i.e., precipitation) on the vegetated soil performances. Under a variety of water supply, xanthan gum with a medium blending content of 0.5% (i.e., with respect to dry soil mass) led to the most substantial improvement in the ability to resist shear loading. This indicates that the appropriate dosage of biopolymer used at the initial stage of plant growth, should provide moderate bond strength between soil particles, whilst not impeding root penetration. Supported by the obtained results, biopolymer is suggested to be used in combination with plants for soil reinforcement for the best efficiency

The role of foam in improving the workability of sand : insights from DEM

Foam as a soil conditioner can transform the mechanical properties of the excavated natural muck and lubricate the interface between the cutting tools and muck, thus reducing the tools’ wear and promoting the efficiency of earth pressure balance (EPB) shield tunneling. This paper aims to explore the meso-mechanism of foam in improving the workability of sand by combining discrete element modeling (DEM) with experimental investigations of slump tests. A “sand-foam” mixture DEM model was generated by simplifying the sand grains and foam as individual particles with different properties. The particle-scale simulated parameters were calibrated based on a series of experimental observations. The effects of foam on the inter-particle contact distribution and the evolution of contact forces during the slumping process were investigated in detail through numerical modeling. It was found that injecting foam into sand specimens could increase the coordination number and the contact number around sand grains. Although the force transmission pattern changes from “sand-sand” into the coexistence of “sand-foam”, “sand-sand” and “foam-foam” contacts, the magnitude of contact forces transferred by foam particles is significantly lower than that by sand particles. The presence of foam reduces contact-scale frictional strength and thus reduces the stability of the microstructures of sand. In addition, the normal direction of inter-particle contact force deflects from the vertical to the horizontal and the magnitude of contact force decreases significantly with the influence of foam

White Matter Abnormalities in Major Depression: A Tract-Based Spatial Statistics and Rumination Study

Increasing evidence indicates that major depressive disorder (MDD) is usually accompanied by altered white matter in the prefrontal cortex, the parietal lobe and the limbic system. As a behavioral abnormity of MDD, rumination has been believed to be a substantial indicator of the mental state of the depressive state. So far, however, no report that we are aware of has evaluated the relationship between white matter alterations and the ruminative state. In this study, we first explored the altered white matter using a tract-based spatial statistics (TBSS) method based on diffusion tensor imaging of 19 healthy and 16 depressive subjects. We then investigated correlations between the altered white matter microstructure in the identified altered regions and the severity of ruminations measured by the ruminative response scale. Our results demonstrated altered white matter microstructure in circuits connecting the prefrontal lobe, the parietal lobe and the limbic system (p<0.005, uncorrected), findings which support previous research. More importantly, the result also indicated that a greater alteration in the white matter is associated with a more ruminative state (p<0.05, Bonferroni corrected). The detected abnormalities in the white matter should be interpreted cautiously because of the small sample size in this study. This finding supports the psychometric significance of white matter deficits in MDD

Effect of sand on the vacuum consolidation of dredged slurry

Vacuum preloading is often used to improve the geotechnical properties of dredged slurry. Although the performance of this method has improved with rapidly developing technology, soil columns usually formed on the drainage boundary induce the decrease of permeability around the boundary, thereby limiting the further development of this method. To address this issue, this paper proposes a method for pretreating the slurry combined with sand prior to vacuum consolidation. This method partially replaces the fine particles with sand to reduce the formation of soil columns. Two groups of vacuum preloading tests were performed to investigate the effect of sand content and sand grain size on the vacuum consolidation of dredged slurry. The test results revealed that for a given sand grain size, increasing the sand content of the sand-slurry mixture increased the pore water drainage and accelerated the dissipation of pore water pressure, thereby increasing the vane shear strength. In contrast, for a constant sand content, the samples containing coarse sand exhibited increased pore water drainage and accelerated dissipation of pore water pressure, thereby increasing the vane shear strength of the soil

Effect of slickwater-alternate-slurry injection on proppant transport at field scales : a hybrid approach combining experiments and deep learning

Proppant transport in underground fractures plays a key role in mitigating sand screen-out and enhancing the stimulated production for hydraulic fracturing. The effects of field pumping schedules, however, are not fully studied. We investigate the effect of slickwater-alternate-slurry injection on proppant transport at field-practical scales. A new hybrid approach is proposed to directly connect experimental studies with field operations, which consists of observation experiments, calculations, and deep learning (DL) workflow. The experiments reveal that the alternate injection induces the unexpected proppant ridge. The modified calculations (considering the ridge height) are proposed to extract features for training the DL algorithm. The workflow predicts the downhole pressure (mainly governed by proppant injection) for error analyses. Approximately 20.2% of the error is eliminated by considering the proppant ridge, thus demonstrating its effect on proppant injection. The predictions are significantly improved in early and late periods of fracturing operations when the fracture is initially created and highly filled. The sensitivity analysis suggests that the pump rate may dominate the ridge height compared with other hydraulic parameters. The study of proppant ridge complements the mechanisms of proppant transport, which is essential for controlling fracturing pressure and boosting the proppant injection

Effects of Billet-Making Methods on Volatile Flavor Components of Sanhua Plum Fruit Billets Based on Headspace-Gas Chromatography-Ion Mobility Spectroscopy and Electronic Nose

In order to investigate the effect of billet-making methods on the volatile components of the Sanhua plum fruit billets, electronic nose and headspace-gas chromatography-ion mobility spectroscopy (HS-GC-IMS) were used to analyze and compare the volatile components of four groups of samples of salt cured, sulfite mixed salt cured, lactic acid bacteria fermented fruit billets and fresh fruit control. The results showed that both the electronic nose linear discriminant analysis (LDA) and the principal component analysis based on the HS-GC-IMS assay results clearly distinguished the four groups of samples, the flavor characteristics of fresh fruits were significantly changed after different curing treatments, and the differences among fruit blanks samples were significant. HS-GC-IMS detected and identified a total of 49 volatile compounds in four groups of samples, and the high relative contents were mainly alcohols, esters and aldehydes. The relative odor activity value (ROAV) showed significant differences in key flavor substances among the three fruit billets, the lactic acid fermented fruit billet had the highest total peak volume of volatile flavor substances (194760) and the most types of key flavor substances (10), mainly short-chain aldehydes. From the perspective of flavor richness of fruit billets, the flavor quality of fruit billet by lactic acid fermentation was considered to be better. The results of this study provided an useful reference for the selection of the billet-making methods of Sanhua plums