Understanding the dynamic process of epitaxial microstructure forming in laser additive manufacturing is very important for achieving products with a single crystalline texture. Here, we perform in ...situ, real-time synchrotron Laue diffraction experiments to capture the microstructural evolution of nickel-based single-crystal superalloys during the rapid laser remelting process. In situ synchrotron radiation Laue diffraction characterises the crystal rotation behaviour and stray grain formation process. With a complementary thermomechanical coupled finite element simulation and molecular dynamics simulation, we identify that the crystal rotation is governed by the localised heating/cooling heterogeneity-induced deformation gradient and recognise that the sub-grain rotation caused by rapid dislocation movement could be the origin of granular stray grains at the bottom of the melt pool.
It is well known that the volumetric block proportion (VBP), to a large extent, dominates the mechanical properties of the soil-rock mixture (S-RM). In this study, random convex polyhedrons were ...applied for simulating rock blocks. Random structural models of S-RMs were generated based on the statistical regularities of volumetric proportion, size, shape, and spatial distributions of rock blocks. Then numerical simulation of triaxial compression tests was conducted sufficiently for studying the influence of VBP on the mechanical properties of virtual S-RM. Results indicate that the VBP indeed poses a major influence on the S-RM's mechanical properties. A high VBP will always lead to a more significant improvement in the strength and deformation parameters. There is an approximate quadratic polynomial relationship between uniaxial compression strength (UCS), elastic modulus, and VBP, while a linear piecewise relationship between internal friction angle, cohesion and VBP. The formulas for the mechanical parameters of S-RM regarding VBP are finally summarized and discussed in detail.
•Numerical triaxial compression tests for 3D random S-RM were conducted.•Influences of VBP on mechanical properties of S-RM were discussed.•Formulas of UCS, E, c and φ related to VBP were summarized.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
Carbon dots (CDs) usually emit a strong blue light and excitation wavelength dependent long wavelength lights. This significantly limits their applications because one has to use a series of ...different excitation light sources to get different colors and the long wavelength emissions are usually very weak. We found that one type of CDs synthesized from p-phenylenediamine could emit various long wavelength lights (green to red) independent of the excitation wavelength when dispersed in different solvents. The photoluminescence quantum yields of the same CDs were 10-35% in different solvents for different color emissions. Based on this solvent-color effect, we further mixed the same CDs with different polymers to form solid CD films for various color emissions, and these film emissions were also excitation wavelength independent. Multicolor LEDs were demonstrated with the same CDs in solution and solid film states for color displays.
Colloidal lead halide perovskite nanocrystals (NCs) have high tunability in the visible light region and high photoluminescence quantum yields (PL QYs) for green and red emissions, but bright blue ...emission is still a challenge. Super small CsPbBr3 perovskite NCs emit blue light around 460 nm with a narrow peak width, and they do not have the problem of phase separation like their Cl–Br counterparts. However, the blue emission from super small CsPbBr3 NCs easily becomes green over time, and their PL QY is still low. The doping of Sb3+ ions successfully reduced the surface energy, improved the lattice energy, passivated the defect states below the band gap, eventually boosted the PL QY of blue emission to 73.8%, and resulted in better spectral stability even at elevated temperatures in solution (40–100 °C). Its CIE coordinates were (0.14, 0.06), which are close to the primary blue color (0.155, 0.070) according to the NTSC TV color standard.
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IJS, KILJ, NUK, PNG, UL, UM
The high moisture content and low strength of dredged soft soils result in significant difficulties in directly reutilizing them in engineering. Improving their mechanical properties effectively and ...achieving re-utilization with the maximum benefit in engineering is the key to disposing of dredged soils with high moisture content. This study investigated the influences of cement and steel slag ratio, moisture content, the maximum particle size of steel slag, and curing age on the compressive strength of dredged silty clay in a plastic flow state. The performance improvement of dredged silty clay stabilized with cement and steel slag was discussed by comparing to related previous studies. The strengthening mechanism of dredged soils stabilized with cement and steel slag was explored by microstructural observation. The results show that when the ratio of cement to steel slag was 9:6; namely, using steel slag to replace 40% of cement, the strength properties of dredged silty clay stabilized by cement and steel slag could ensure the minimum requirements of the project greater then 100 kPa, and their economics could achieve the best results. The finer the particle size of steel slag was, the better the stabilization effect was. The compressive strength of dredged silty clay stabilized by cement and steel slag with particle sizes of less than 0.075 mm was 1.06 times, 1.10 times, and 1.16 times that of 0.25 mm, 1 mm, and 2 mm and increased linearly over curing ages earlier than 28 days. The compressive strength of dredged silty clay stabilized by cement and steel slag cured for 28 days was 2.44 times, 1.59 times, and 1.36 times that of 3, 7, and 14 days, respectively. The evolution of microstructural characteristics showed that the internal pore sizes of dredged soil decreased the structural compactness increased significantly due to the formation of more calcium silicate hydrate and other agglomerated flocculent gel materials from the further reaction between steel slag and cement hydration products. The results of this study can provide technological parameters for the re-utilization of dredged soil stabilized with cement and steel slag.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The cemented soils by trench cutting re-mixing deep (TRD) wall or trench cutting assembled diaphragm (TAD) wall are a mixture of various soils. The physical and mechanical properties of these ...cement-stabilized soils are thus not only affected by construction technologies but also significantly controlled by cement content and soil texture. Three typical soils, including clay soil, silty soil, and fine sand, were used to prepare samples of cement-stabilized soils with different combinations of cement content and soil texture. Then, the workability (including fluidity, cohesion, and water retention), strength, hydraulic, and microstructure characteristics of different cement-stabilized soils were investigated by depth compression, permeability, and microstructural tests. Results indicate that there should be a higher water-cement ratio for clay soil while a low value for fine sand to achieve the required compactness. The unconfined compressive strength of cement-stabilized soils increased linearly with cement content, while their permeability had an approximate power relationship with cement content. The permeability magnitude of cement-stabilized composite soils was greatly affected by the proportion of the soil with high permeability. The clay soil could partly improve the pore structure of cement-stabilized composite soils and reduce permeability due to fine particles’ high activity, which was further confirmed by the microstructural analysis. The relationship between unconfined compressive strength and permeability coefficient was approximately consistent with a power function. The unconfined compressive strength of cement-stabilized soils decreased linearly with porosity, and the logarithm to base 10 of permeability coefficients of cement-stabilized soils increased with porosity.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Perfluorinated compounds (PFASs) are a new artificial chemical. Due to its substantial toxicity and complex degradation in the natural environment, monitoring PFASs has become a hot issue for many ...researchers. Currently, the relationship between the concentration of PFASs in serum and the concentration of PFASs in drinking water is unclear. This paper aims to study the concentration levels of PFASs in drinking water and residents' serum in a city in northern China and the relationship between them. The results show that the concentration of PFASs in drinking water is low, and the average concentrations of perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS) were 2.57 ± 0.69 ng/L and 0.30 ng/L, respectively, which were lower than the limits specified in China's newly introduced Standards for drinking water quality (GB 5749-2022). In the serum of residents, PFOA and PFOS were the two PFASs with the highest concentration. Spearman correlation analysis showed that perfluorohexane sulfonate (PFHxS) and PFOS concentrations were positively correlated with age, and PFHxS, PFOA, PFNA, and PFOS varied with sex. At the same time, the correlation analysis also showed no correlation between PFAS in drinking water and serum, indicating that drinking water was not the main factor causing the physical burden of PFAS in residents. The HI method was used to assess the health risks of PFASs to human beings. The risk entropy of all PFASs for human hepatotoxicity and reproductive toxicity is below 1.
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•The concentration of PFASs in Beijing drinking water is lower than most limits.•PFOA and PFOS are the two most abundant PFASs in the serum of Beijing residents.•Drinking water is not a significant contributor to the burden of PFASs on Beijing residents.•The risk entropys of all PFASs for hepatotoxicity and reproductive toxicity are <1.0.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
Enhancing strength performance while reducing cement consumption for soil stabilization is the key to improving the economic benefits of engineering construction projects like retaining structures of ...underground engineering, subgrade bases, and foundation reinforcement. This study employed metakaolin as the additive to realize these two aims. A series of compression and microstructural observation tests on cement- and metakaolin-stabilized fine sandy soils (CMSFSS) were conducted with different cement–metakaolin ratios, water–binder ratios, dosages of the binder (the mixture of cement and metakaolin), and curing ages. The influences of these factors on the mechanical performance of the CMSFSS were studied. The empirical relationships between compressive strength and these influence factors were discussed. Then, the strengthening mechanism of the CMSFSS at different curing ages was investigated. The results showed that the optimal cement–metakaolin ratio for fine sandy soil stabilization was 5:1, which did not change with the total consumption of cement and metakaolin. The compressive strength of the CMSFSS decreased linearly with the water–binder ratio but increased linearly with the curing age. Four empirical prediction formulas about these strength-influencing factors were summarized. The evolution of microstructural characteristics discovered by scanning electron microscope and mercury intrusion tests showed that the hydrated gels in CMSFSS were being formed during the early curing age and resulted in decreasing pore sizes with an initial rapid rate and then a slower rate over the curing age. The gradual disappearance of calcium hydroxide (by-products of cement hydration) over the curing age proved the promoting effect of metakaolin on the strength improvement of cement-stabilized fine sandy soils. This study can provide a reference for applying cement and metakaolin in soil stabilization practices.
Silicon-rich anodes are desired to leverage the energy capacity of lithium-ion batteries (LIBs) towards critical markets. We prepared new silicon-rich composite anodes with a nanofiber-in-microfiber ...architecture using a co-axial electrospinning setup. A polyvinyl alcohol (PVA) solution that allows high silicon content serves as the central stream, which holds silicon nanoparticles into short, branched composite nanofibers. These nanofibers were wrapped by long, ductile microfibers made of polyacrylonitrile (PAN) that is supplied in the sheath fluid. After carbonization, the received carbon/silicon composites were tested as the anode of LIBs, in which the silicon-rich nanofibers host the majority of lithium ions while their thin carbon skin originated from PVA promotes the conductivity and charge transfer. The outside PAN-derived microfibers provide needed structural support for those encapsulated silicon-rich nanofibers, making the final composites also an integrated, three-dimensional current collector. The nanofibrous morphology and the void space in between help accommodate the notorious volume expansion issues during lithiation/delithiation. The new composites were confirmed on their nanofiber-in-microfiber configuration. With a Si content of 40%, this unique fibrous anode material achieves ∼900 mAh g−1 specific capacity and ∼90% capacity retention from cycle 50 to cycle 250 by effectively balancing some major challenges associated with silicon-rich anodes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
The structure and mechanical properties of the stomatopod dactyl club have been studied extensively for its extreme impact tolerance, but a systematic in situ investigation on the multiscale ...mechanical responses under high‐speed impact has not been reported. Here the full dynamic deformation and crack evolution process within projectile‐impacted dactyl using combined fast 2D X‐ray imaging and high‐resolution ex situ tomography are revealed. The results show that hydration states can lead to significantly different toughening mechanisms inside dactyl under dynamic loading. A previously unreported 3D interlocking structural design in the impact surface and impact region is reported using nano X‐ray tomography. Experimental results and dynamic finite‐element modeling suggest this unique structure plays an important role in resisting catastrophic structural damage and hindering crack propagation. This work is a contribution to understanding the key toughening strategies of biological materials and provides valuable information for biomimetic manufacturing of impact‐resistant materials in general.
Multiscale structural and mechanical characterization of stomatopod cuticle under in situ spherical projectile penetrating loadings. In this work the full dynamic crack evolutionary process and other toughening mechanisms inside the dactyl club under high‐speed impact were uncovered.
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FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
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