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The development of high-speed aerial vehicles urgently requires high-performance integrated materials for ablation resistance, thermal insulation and oxidant protection under high temperature. The previously prepared carbon aerogel composites (C/CA), with ultra-high temperature thermal insulation properties, were impregnated with SiCO precursor sol and pyrolysed in nitrogen atmosphere at 1200°C. The impregnation/pyrolysis process was performed once, twice and thrice to obtain three different C/C-SiCO nanoporous ceramic composites. Further, TaSi2-MoSi2-borosilicate glass (TM-BG) coating or TaSi2-MoSi2-ZrB2-borosilicate glass (TMZBG) coating was prepared on the surface of the C/C-SiCO through slurry brushing combined with graphite powder embedded sintering process. By simulating the actual application environment through oxygen acetylene flame ablation test, the ablation resistance of the samples was studied and their oxidation mechanism was analysed. The results show that the ablation rate of the C/C-SiCO after 200 s ablation at 1600 °C decreases with the increase of the number of impregnation/pyrolysis steps and that the ablation resistance of the coating modified C/C-SiCO was significantly enhanced. The addition of ZrB2 to the coating improves the compatibility between the substrates and the coating, and the TMZ-BG coated sample has better ablation resistance. At high temperature, the borosilicate glass in the coating is in a viscous flow state. Meanwhile the SiO2 generated by the oxidation of other silicide raw materials forms a dense glass layer on the coating surface, which can be used as an oxygen barrier to provide better protection for the substrates. The coating-modified C/C-SiCO porous ceramic composites are expected to be used as a high-temperature ablation-resistant material for the thermal protection system of new aerospace vehicles.

SUMMARY: Domestication has dramatically increased crop size and biomass, reflecting the enhanced accumulation of photosynthates. However, we still lack solid empirical data on the impacts of domestication on photosynthetic rates at different light intensities and on leaf anatomy, and of the relationships of photosynthesis with aboveground biomass. In this study, we measured the photosynthetic rate at three photosynthetic photon flux densities of 2000 (high), 1000 (moderate) and 400 μmol m−2 sec−1 (low light intensity), dark respiration, relative chlorophyll content (SPAD), leaf morphology, and aboveground biomass in 40 wild, 91 semiwild, and 42 domesticated cotton genotypes. The study was replicated for two years (growing years 2018 and 2019). During the first domestication stage (transition from wild to semiwild genotypes), domestication led to higher photosynthetic rates measured under high light intensity, higher SPAD, larger leaf area (LA), and lower leaf mass per unit area (LMA), contributing to greater aboveground biomass accumulation in both study years. During the second domestication stage (transition from semiwild to domesticated genotypes), domestication significantly enhanced photosynthesis under low light intensity and reduced LMA, which were associated with increased aboveground biomass in both study years. In conclusion, photosynthesis improvement at different light intensities has been a gradual domestication phase specific process with the rate of photosynthesis enhanced under high light during the first domestication stage, and under low light during the second domestication stage. We argue that these differences reflect a higher proportion of LA photosynthesizing under low light due to enhanced canopy expansion at the second domestication stage. Significance Statement: Photosynthesis improvement at different light intensities has been a gradual domestication phase specific process with the rate of photosynthesis enhanced under high light during the first domestication stage, and under low light during the second domestication stage. [ABSTRACT FROM AUTHOR]

Efficient initiation of oblique detonation waves (ODWs) is crucial for optimizing the performance of oblique detonation wave engines. A novel approach is proposed for enhancing ODW initiation through expansion waves in this research. Validation of the expansion wave-reinforced initiation method is conducted via numerical simulations employing multi-species reactive Euler equations and a pressure-dependent reaction mechanism. Results demonstrate a significant reduction in the initiation length of ODWs with the addition of an expansion wave ahead of the wedge, contrasting with the absence of detonation wave initiation on a wedge lacking an expansion wave. A theoretical model, based on expansion wave and shock wave relations, along with constant volume combustion theory, elucidates the underlying mechanism of reinforcement. The model reveals that crossing the expansion wave elevates the fluid's Mach number and locally enlarges the flow deflection angle on the wedge surface, without altering the wedge's structure. Furthermore, post-shock temperature increases and pressure decreases compared to the wedge not encountering an expansion wave. The heightened temperature predominantly triggers ODW initiation, thus reinforcing the process. Theoretical analyses indicate the reinforcement's greater efficacy at lower inflow temperatures and lower inflow Mach numbers, suggesting the expansion wave's suitability for initiation in the early flight stages of an aircraft equipped with oblique detonation wave engines. [ABSTRACT FROM AUTHOR]