Porous high-entropy carbide ceramics (PHECs) exhibit excellent high-temperature stability and are considered promising candidates for thermal-protection applications. However, their interconnected pore structure facilitates oxygen ingress during ablation, resulting in accelerated oxidation and structural degradation. In this work, a gradient SiC-rich dense surface layer was constructed on porous (Ta0.2Nb0.2Ti0.2Zr0.2Hf0.2)C ceramics through phenolic-resin infiltration, carbonization, and reactive melt infiltration (RMI) of silicon. The resulting composites exhibited a hierarchical architecture consisting of a dense SiC-rich surface layer and a porous interior. The initial pore structure strongly influenced molten-Si infiltration and reaction behavior, leading to an increase in the thickness of the SiC-rich dense layer from 33.3 to 121.2 μm with increasing porosity. During ablation, oxidation of SiC generated SiO2, which interacted with refractory transition-metal oxides to form a SiO2-rich composite oxide layer that effectively suppressed oxygen diffusion and enhanced oxidation resistance. Consequently, the oxide-layer thickness decreased from 121.4 to 35.2 μm, accompanied by a significant reduction in the mass ablation rate. Among all samples, HEC-SiC5 exhibited the best ablation resistance, with a mass ablation rate as low as 0.23 mg/s. This work establishes a direct correlation between substrate pore architecture, molten-Si infiltration behavior, dense-layer evolution, and ablation resistance, providing a practical strategy for the design of lightweight porous HEC-based thermal-protection materials.
Considering the 518 km middle stretch of the Ganga River, we conducted in-situ and controlled incubation studies from 2021 to 2024 to investigate carbon degradation-driven biogeochemical changes in the river constrained by climate warming and atmospheric deposition of nutrients. High concentrations of labile (415.70 µg·C·g−1) and recalcitrant (231.30 µg·C·g−1) carbon fractions coupled with extracellular enzyme activities and CO2 emissions (up to 270 mg·m−2·h−1) indicated microbial degradation and, consequently, dissolved oxygen depletion (≤2 mg·L−1) at polluted sites. The combined influence of atmospheric nutrient loading, hypoxia-driven sediment-P release, and denitrification associated nitrogen loss, shifts N:P ratios of river water and sediments. Warming altered the redox conditions at sediment-water interface, enhancing microbial extracellular enzyme activities and CO2 emission (up to 24% at +2 °C). However, it caused a decline in microbial apparent carbon use efficiency. The study shows that the multi-stressors synergy and associated feedbacks progressively destabilizes riverine stoichiometric balance with a likely switch over to N or P limitation and ecological functioning. Our study highlights that the watershed-scale nutrient loading and climate-sensitive biogeochemical transformations jointly regulate oxygen-dependent nutrient cycling in large rivers, emphasizing the need for integrated river-watershed management under a changing climate scenario.
Fucosylated human milk oligosaccharides are valuable targets for microbial biomanufacturing. Here we engineered the probiotic Escherichia coli Nissle 1917 as a versatile chassis for synthesizing both 2′-fucosyllactose and 3-fucosyllactose. We implemented lactose preservation and blocked colanic acid precursor consumption while reinforcing the de novo GDP-L-fucose pathway. This core module was coupled with either WbgL or FutM2 to drive terminal fucosylation. Initial screening yielded a 2′-fucosyllactose titer of approximately 1.21 g/L. Integrating an additional chromosomal wbgL cassette increased the titer to approximately 1.58 g/L, whereas subsequent genomic modifications did not further improve the 2′-FL titer. Cultivation with 30 g/L glycerol and 5 g/L yeast extract significantly improved productivity, enabling the strain to produce approximately 7.71 g/L of 2′-fucosyllactose in shake-flask cultures. Conversely, the FutM2 strain produced 0.38 g/L 3-fucosyllactose without yeast extract and nutrient supplementation unexpectedly suppressed product accumulation despite promoting biomass formation. The work provides a probiotic-chassis proof of concept and identifies product-module physiology as a priority for further engineering.
The molecular parameters of polyethylene are characterized by its molecular weight distribution and the branching. Both strongly manipulate the crystalline state, which plays a key role in the predetermination of many product properties such as gas solubility, melting behavior, and tensile strength. This work addresses the question of how the crystallinity of polyethylene can be calculated as a function of molecular parameters (molecular weight and branching) and temperature. The basic idea is to transfer the so-called statistical car-parking problem (CPP) to polyethylene. However, this concept does not consider branching. Therefore, the CPP is coupled with the Flory approach for co-polymers (FCA), which explicitly considers branching. The coupled theory of CPP and FCA correctly predicts the crystallinity of branched polyethylene from molecular parameters and temperature, and reproduces the dependencies of the influencing variables observed in experimental data reported in the literature.
Surface mechanical attrition treatment (SMAT) has been used to treat the surfaces of an aluminium alloy manufactured by selective laser melting (SLM). SMAT involved impacting the SLM sample surface with spherical balls at a frequency of 30 Hz for 10 min to 30 min, which induced plastic deformation of the sample surface, leading to a change in surface finish and surface hardness. The surface finish, morphology, hardness, and structural features have been investigated. The results show that SMAT is very effective in improving the surface finish of the SLM aluminium alloy surface. After 30 min of treatment, the roughness value (Ra) was reduced by 87%, from 19.4 μm to 2.6 μm. SMAT also has the benefit of increasing the surface hardness of SLM aluminium alloy from 125 HV0.1 to 160 HV0.1, and generating a strain hardened layer of about 300 μm thick at the subsurface, and thus has the potential of improving wear resistance. In addition, SMAT induced a compressive residual stress of around 100 MPa on the treated surface, which would be beneficial in improving the fatigue properties of SLM aluminium alloy. The mechanisms underlying surface smoothing, hardness increase, and the evolution of compressive residual stress in SMAT are discussed in terms of severe surface plastic deformation and strain hardening.
