The Ediacaran-Cambrian (E-C) transition period marks a pivotal juncture in Earth's history, characterized by profound geological events, dramatic environmental changes, and the enigmatic "Cambrian Explosion", whose synergistic relationship remains elusive. The coincidence of biotic extinction during the E-C period with negative carbon isotope excursions (NCIEs) is not well understood. This study employed analyses of organic carbon isotopes (delta C-13(org)), carbonate carbon isotopes (delta C-13(carb)), and nitrogen isotopes (delta N-15) alongside the major and trace element analyses on samples from a well in the Yangtze Block, South China. The results reveal three NCIEs during the early Cambrian (Fortunian to Stage 2), with maximum negative values of -38.50 parts per thousand (delta C-13(org)) and - 17.8 parts per thousand (delta C-13(carb)), coupled with a positive delta N-15 value of 4.66 parts per thousand. The delta C-13(org) and delta N-15 values subsequently shifted to approximately -32 parts per thousand and similar to 0 parts per thousand, respectively, during the early to middle Stage 3. The redox-sensitive trace elements (RSTEs) and Ce/Ce* values indicate that the Fortunian-early Stage 2 interval was characterized by a suboxic-oxic environment, whereas Stage 3 maintained an anoxic-euxinic condition. The Co (ppm) x Mn (%) proxy indicates strong upwelling activity from the Fortunian to early Stage 3, which weakened after the middle Stage 3. Based on the covariance between the isotopic record and the marine environment, we propose that the NCIEs during the early Cambrian were originated from the C-13-depleted dissolved organic carbon (DOC) exported by upwelling to the shallow shelf where denitrification was fueled in oxygen minimum zones (OMZs) to enrich the dissolved inorganic carbon (DIC) with depleted C-13 in the surface water, and while the more positive delta C-13 trend in Stage 3 reflects an enhanced anoxia environment or a diminished upwelling intensity. Oceanic nitrate acts as an oxidant of DOC and retards oceanic O-2 depletion during aerobic respiration. Concurrently, elevated DIC derived from DOC facilitated skeletal mineralization, whereas upwelling-supplied nutrients (e.g., phosphorus) further promoted eukaryotic proliferation from the Fortunian to Stage 2. This study introduces a novel mechanistic framework for the NCIEs during the E-C period, highlighting the inner link between carbon and nitrogen cycles, which offers further perspectives to unravel the complexity underlying the "Cambrian Explosion".
Spray flashing is a key technology in polymer devolatilization, capable of releasing solvents from polymers, as well as separating gases and liquids in flash tanks for solvent recovery. This paper establishes a simulation method for the flash devolatilization of high-solvent-content polymers based on the Eulerian-Lagrangian multiphase flow model; this method incorporates flash phase-change and viscosity correction models. The numerical simulations align well with the results of spray flash evaporation experiments. The polymer and solvent distribution patterns at different times in the tank are obtained through simulations, and corresponding structural improvement schemes are proposed. According to the results, near the nozzle holes, solvent evaporation decreases the phase content and expands the droplets. In the upper part of the tank, the number of droplets is substantial, exhibiting severe gas-liquid entrainment. At different spray angles, the droplet distribution areas at any given time are distinct; a larger spray angle accelerates droplet diffusion, increasing the number of droplets at the top. The installation of an annular baffle reduces gas-liquid entrainment by 89.84 %, whereas the placement of an annular hot oil barrel and a corrugated wall enhance devolatilization efficiency by 5 % and 12 %, respectively. These improvements can enhance flash devolatilization and improve product performance. Therefore, exploring the enhancement of flash devolatilization efficiency offers practical engineering significance for the design of front-end devolatilization equipment.
Silicon monoxide (SiO), a high-capacity anode material, suffers from low initial coulombic efficiency (ICE), poor electrical conductivity, and severe volume expansion, which limit its electrochemical performance. To address these challenges, we developed an innovative SiO/LixSiyOz/G@C composite through a multi-faceted modification strategy that incorporates lithium silicate (LixSiyOz), integrates graphene, and applies conformal carbon coating. Notably, we demonstrate that graphene oxide serves a dual function: (1) as a reaction template directing the crystallization of electrochemically active Li2Si2O5 and (2) in constructing a 3D conductive network with pyrolytic carbon. The resultant composite architecture delivered exceptional electrochemical performance, exhibiting an 18 % enhancement in ICE, remarkable rate capability (673 mAh g-1 at 2C-representing a threefold improvement over pristine SiO), and outstanding cycling stability with 97 % capacity retention after 200 cycles at 0.5C. The LixSiyOz layer was lithiated in situ on SiO via a thermal reaction with Li2CO3 in the presence of graphene oxide, followed by asphalt-derived carbon coating to further boost conductivity and stability. This study presents a comprehensive and scalable approach for engineering high-performance SiO-based anodes, offering valuable insights into the design of next-generation battery materials.
Creep-fatigue tests were conducted on Inconel 617 alloy at 700 degrees C. Effects of strain hold modes including tension hold (TH), compression hold (CH), and tension-compression mixed hold (TC) were studied at different strain amplitudes. The material consistently presented the two-stage hardening and a final rapid softening behavior under different hold modes. Under different hold modes, the dynamic strain aging was most pronounced in TH mode, weaker in CH mode, and weakest in TC mode. This variation stemed from solute atom diffusion and dislocation pinning-unpinning. The grain diameters in post-test specimens under different hold modes followed the order: TH > TC > CH, which was related with the occurrence of grain boundary migration and dynamic recrystallization. The oxidation damage differences characterized by the thickness of oxide layers on the longitudinal section were identified to follow the sequence of TC > TH > CH. Correspondingly, the embrittled grain boundaries caused by the oxidation damage led to the intergranular crack initiation in the TH and TC tests, while the crack initiated in the transgranular behavior in the CH tests. Based on the experimentally observed difference between tension and compression hold damage, damage mode factors were proposed to reasonably evaluate the differences in damage contribution of various strain hold modes. Furthermore, the factors were introduced to the classical time fraction model to achieve a significant improvement in life prediction, with all life data falling into the scatter band of 1.5.
Ammonia, as a carbon-free fuel, offers great potential for reducing carbon emissions through co-combustion with hydrocarbons such as methane. However, in practical combustion systems, high concentrations of CO2 and NO resulting from staged combustion or flue gas recirculation (FGR) can significantly affect flame propagation and pollutant formation. In this work, the temperature, OH radical and NO distribution in laminar planar NH3/CH4/O2/NO/CO2 premixed flames established in a heat flux burner under various equivalence ratios and ammonia blending ratios were investigated using the ultraviolet broadband absorption spectroscopy (UVBAS) technique. The results confirm the accuracy of UVBAS in regions with mild gradients (e.g., post-flame zones) and successfully capture the dual role of NO—acting as an oxidizer in the pre-ignition zone and rapidly forming as the primary nitrogen oxide beyond the flame front. One-dimensional laminar flame simulations based on detailed chemical kinetic mechanisms were performed to validate the experimental data and analyze reaction pathways. While most mechanisms show good agreement in predicting laminar burning velocities (SL) and OH profiles, significant discrepancies remain in NO formation predictions. Based on sensitivity and rate-of-production (ROP) analyses combined with experimental measurements, key reaction sub-mechanisms were refined and improved.
