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In order to improve the stability of air bubbles in fresh concrete, it is of great significance to have a better understanding of the mechanisms and main influencing factors of bubble stability. In the present review, the formation and collapse process of air bubbles in fresh concrete are essentially detailed; and the advances of major influencing factors of bubble stability are summarized. The results show that the surface tension of air–liquid interface exerts a huge impact on bubble stability by reducing surface free energy and Plateau drainage, as well as increasing the Gibbs surface elasticity. However, surface tension may not be the only determinant of bubble stability. Both the strength of bubble film and the diffusion rate of air through the membrane may also dominate bubble stability. The application of nano-silica is a current trend and plays a key role in ameliorating bubble stability. The foam stability could be increased by 6 times when the mass fraction of nano-particle reached 1.5%.

This paper studies an impact of media epidemic system with diffusion and linear source. We first derive the uniform bounds of solutions to impact on media reaction diffusion system. Then, the basic reproduction number is calculated and the threshold dynamics of impact media reaction diffusion system is also given and the Kuratowski measure κ of non-compactness is also considered. In addition, assume the spatial environment is homogeneous, it is shown that the unique endemic equilibrium of the system is global stability by constructing suitable Lyapunov function. Finally, we discuss the asymptotic profile of the system when the diffusion rate of the susceptible (infected) individuals for the system tends to zero or infinity. The main results show that the activities of infected individuals can only be at low risk, and then the virus eventually will be extinct, that is, to control the entry of viruses from abroad and increase the detection of domestic viruses. Finally, some numerical simulations are worked out to confirm the results obtained in this paper.

Microstructures and tensile properties are essential for the practical application of nanoporous copper (NPC), especially in areas of high request to pore distribution and tension. In this work, a novel self-supporting NPC foil (NPC@Cu@NPC) was fabricated through alloying-dealloying method in situ. The results showed that the self-supporting structure provided a tensile strength of about 370 MPa for the NPC@Cu@NPC. When the dealloying temperature changed from 323.15 to 363.15 K, the diffusion rate of copper atoms in the dealloying process increased from 8.970 × 10 −17  to 1.610 × 10 −15 m 2 /s, resulting in a significant coarsening of nanoporous ligament along with increase of elongation from 1.53 to 2.73%. The diffusion growth model revealed the quantitative relationship between dealloying temperature (T) and ligament width (d) (ln(d) was proportional to 1/T). The rapid diffusion of copper atoms at high dealloying temperatures could coarsen the ligaments of the nanoporous structure and increase the fracture elongation. In addition, NPC@Cu@NPC had a higher electrochemical active surface area (ECSA) (85.31 cm 2 ) and lower internal charge transfer resistance ( R ct ) (9.97 Ω) than the flat copper foil (ECSA = 3.5 cm 2 , R ct = 71.8 Ω). Thus, NPC@Cu@NPC, with more electrochemical active sites and higher electron transport efficiency, has potential application prospects in electrocatalysis and secondary batteries.

The fractional change in the reaction progress variable gradient depends on the flow normal straining within the flame and also upon the corresponding normal gradients of the reaction rate and its molecular diffusion transport. The statistical behaviours of the normal strain rate and the contributions arising from the normal gradients of the reaction rate and molecular diffusion rate within the flame were analysed by means of a Direct Numerical Simulation (DNS) database of statistically planar turbulent premixed flames ranging from the wrinkled/corrugated flamelets regime to the thin reaction zones regime. The interaction of flame-normal straining with the flame-normal gradient of molecular diffusion rate was found to govern the reactive scalar gradient transport in the preheat zone, where comparable timescales for turbulent straining and molecular diffusion are obtained for small values of Karlovitz numbers. However, the molecular diffusion timescale turns out to be smaller than the turbulent straining timescale for high values of Karlovitz numbers. By contrast, the reaction and hot product zones of the flame remain mostly unaffected by turbulence, and the reactive scalar gradient transport in this zone is determined by the interaction between the flame-normal gradients of molecular diffusion and chemical reaction rates.

The global dynamics of the typical age-structured model with age-dependent mortality and diffusion rates on unbounded domains have been established. On the one hand, we showed that a positive and constant state solution of the mature population is globally asymptotically stable with respect to the compact-open topology; on the other hand, we showed that the trivial solution is globally asymptotically stable with respect to the usual supremum norm. As an application of our result, we applied the result to birth functions appearing in biology. In addition to the theoretical results, we also present a numerical simulation.

Hydrogen peroxide (H 2 O 2 ) synthesis by electrochemical oxygen reduction reaction has attracted great attention as a green substitute for anthraquinone process. However, low oxygen utilization efficiency (<1%) and high energy consumption remain obstacles. Herein we propose a superhydrophobic natural air diffusion electrode (NADE) to greatly improve the oxygen diffusion coefficient at the cathode about 5.7 times as compared to the normal gas diffusion electrode (GDE) system. NADE allows the oxygen to be naturally diffused to the reaction interface, eliminating the need to pump oxygen/air to overcome the resistance of the gas diffusion layer, resulting in fast H 2 O 2 production (101.67 mg h -1 cm -2 ) with a high oxygen utilization efficiency (44.5%–64.9%). Long-term operation stability of NADE and its high current efficiency under high current density indicate great potential to replace normal GDE for H 2 O 2 electrosynthesis and environmental remediation on an industrial scale. H 2 O 2 electrosynthesis has garnered great attention as a green alternative to the anthraquinone process. Here the authors propose a cost-effective cathode to greatly improve the O 2 diffusion coefficient, resulting in a high H 2 O 2 production without the need for aeration.

In the present work, we introduce two new estimators of chaotic diffusion based on the Shannon entropy. Using theoretical, heuristic and numerical arguments, we show that the entropy, S, provides a measure of the diffusion extent of a given small initial ensemble of orbits, while an indicator related with the time derivative of the entropy, S′, estimates the diffusion rate. We show that in the limiting case of near ergodicity, after an appropriate normalization, S′ coincides with the standard homogeneous diffusion coefficient. The very first application of this formulation to a 4D symplectic map and to the Arnold Hamiltonian reveals very successful and encouraging results.

Fast-charging batteries typically use electrodes capable of accommodating lithium continuously by means of solid-solution transformation because they have few kinetic barriers apart from ionic diffusion. One exception is lithium titanate (Li₄Ti₅O12), an anode exhibiting extraordinary rate capability apparently inconsistent with its two-phase reaction and slow Li diffusion in both phases. Through real-time tracking of Li⁺ migration using operando electron energy-loss spectroscopy, we reveal that facile transport in Li4+xTi₅O12 is enabled by kinetic pathways comprising distorted Li polyhedra in metastable intermediates along two-phase boundaries. Our work demonstrates that high-rate capability may be enabled by accessing the energy landscape above the ground state, which may have fundamentally different kinetic mechanisms from the ground-state macroscopic phases. This insight should present new opportunities in searching for high-rate electrode materials.

The meticulous design of advanced electrocatalysts and their integration into gas diffusion electrode (GDE) architectures is emerging as a prominent research paradigm in the H 2 O 2 electrosynthesis community. However, it remains perplexing that electrocatalysts and assembled GDE frequently exhibit substantial discrepancies in H 2 O 2 selectivity during bulk electrolysis. Here, we elucidate the pivotal role of mass transfer behavior of key species (including reactants and products) beyond the intrinsic properties of the electrocatalyst in dictating electrode-scale H 2 O 2 selectivity. This tendency becomes more pronounced in high reaction rate (current density) regimes where transport limitations are intensified. By utilizing diffusion-related parameters (DRP) of GDEs (i.e., wettability and catalyst layer thickness) as probe factors, we employ both short- and long-term electrolysis in conjunction with in-situ electrochemical reflection-absorption imaging and theoretical calculations to thoroughly investigate the impact of DRP and DRP-controlled local microenvironments on O 2 and H 2 O 2 mass transfer. The mechanistic origins of diffusion-dependent conversion selectivity at the electrode scale are unveiled accordingly. The fundamental insights gained from this study underscore the necessity of architectural innovations for mainstream hydrophobic GDEs that can synchronously optimize mass transfer of reactants and products, paving the way for next-generation GDEs in gas-consuming electroreduction scenarios. Electrocatalysts and assembled gas diffusion electrodes frequently exhibit discrepancies in selectivity during H 2 O 2 electrosynthesis. Here, the authors report the pivotal role of key species transport beyond the intrinsic properties of electrocatalysts in dictating electrode-scale H 2 O 2 selectivity.

Carbon dioxide (CO 2 ) electroreduction reaction (CO 2 RR) offers a promising strategy for the conversion of CO 2 into valuable chemicals and fuels. CO 2 RR in acidic electrolytes would have various advantages due to the suppression of carbonate formation. However, its reaction rate is severely limited by the slow CO 2 diffusion due to the absence of hydroxide that facilitates the CO 2 diffusion in an acidic environment. Here, we design an optimal architecture of a gas diffusion electrode (GDE) employing a copper-based ultrathin superhydrophobic macroporous layer, in which the CO 2 diffusion is highly enhanced. This GDE retains its applicability even under mechanical deformation conditions. The CO 2 RR in acidic electrolytes exhibits a Faradaic efficiency of 87% with a partial current density ( j C 2 + ) of −1.6 A cm −2 for multicarbon products (C 2+ ), and j C 2 + of −0.34 A cm −2 when applying dilute 25% CO 2 . In a highly acidic environment, C 2+ formation occurs via a second order reaction which is controlled by both the catalyst and its hydroxide. Carbon dioxide electroreduction in acidic environments has been suboptimal. Here, the authors addressed this issue by designing a gas diffusion electrode with a special metal structure, which achieves efficient electroreduction while conducting a systematic investigation of the underlying mechanism.