As the COVID-19 pandemic recedes, urban life, economic activities, and transportation systems appear to have returned to normal. Yet latent post-pandemic impacts on shifts in socioeconomic stratification within human mobility remain under-explored. Using large-scale longitudinal mobile signaling data for nearly 8 million residents in Beijing between 2019 and 2024, weighted using census data and integrated with social attributes and housing price data, this study examines how socioeconomic stratification patterns and mobility behaviors evolve across socioeconomic groups. Here, we show that the potential stratification has intensified in the post-pandemic era. First, the place-level and inter-group contact-based socioeconomic stratification index increased by 34.83% and 32.34%, respectively. Counterfactual simulations reveal that shortened travel distances and homogeneous mobility preferences reduced opportunities for cross-group encounters. Second, residential proximity and shared social attributes significantly explain variations in opportunities for inter-group co-presence. Spatial disparities in urban infrastructure configuration can either mitigate or reinforce mobility-related socioeconomic stratification across locations. Collectively, this study underscores that spatial context, socioeconomic characteristics, and behavioral preferences shape mobility stratification, offering empirical evidence for understanding post-pandemic socioeconomic stratification dynamics.
Abstract This study aims to enhance ultrahigh performance concrete (UHPC) by modifying steel fibers with graphene oxide (GO). The electrophoretic deposition (EPD) method was employed to coat GO onto steel fiber surfaces, with investigations focused on GO modification effects on fiber-matrix interfacial properties and UHPC mechanical performance. The results demonstrate that GO deposition significantly improves fiber-matrix interface properties. The 30-min EPD treatment increased the average interfacial bonding strength and equivalent bonding strength by 22.1% and 11.1%, respectively. Given the enhancement of interface shear stress, the failure plane shifted toward the matrix side, whereas periodic groove structures formed along the inner walls of pulled-out fiber channels. This phenomenon is attributed to the physical-chemical synergistic interface strengthening arising from the rough surface morphology of GO coating and the chemical bonding with hydration products. Benefiting from the improved interface properties, GO-modified steel fibers enhanced the tensile strength ( σ p c ), tensile energy absorption capacity ( g - value ), and flexural strength of UHPC by 8.5%–17.6%, 28.8%–75.0%, and 27.6%–38.9%, respectively. Due to the declining nanoparticle deposition efficiency caused by long-term EPD treatment, the performance enhancements exhibited a nonlinear decay pattern with extended EPD treatment duration.
This study presents a novel variational-based numerical algorithm for simulating time-scale non-migratory Birkhoffian systems. Birkhoffian mechanics provides a unified framework for describing a broad class of dynamical systems, including autonomous, non-autonomous, and nonholonomic types. Although migratory and non-migratory systems are equivalent in the continuous setting, the non-migratory system is particularly necessary on discrete time scales because it remains naturally compatible with the classical discrete Birkhoffian variational framework and thus provides a more suitable basis for structure-preserving computation. Within this framework, discrete dynamical equations are derived from a non-migratory variational principle. Based on the discrete Pfaff-Birkhoff principle, the time-scale Birkhoff’s equations are obtained. Furthermore, definitions and criteria for discrete Noether symmetry and quasi-symmetry are introduced, leading to the derivation of associated conserved quantities. The effectiveness of the algorithm is verified through numerical simulations of the damped oscillator and the Hojman-Urrutia model. This proposed method offers a unified, structure-preserving numerical solution for continuous and time-scale non-migratory systems, and inherently supports variable step size computations, thereby enhancing its practicality in simulations.
Refractory wastewater treatment via Fenton reactions is hindered by iron sludge. Herein, fluorinated UiO-66(Zr)-F4 was employed as a hydrogen-storage carrier to confine Pd⁰ catalytic centers, and an [H]-mediated (H2-precursored) Fenton-like system was constructed for carbamazepine degradation under ambient conditions. With 25 μM Fe2 + and 60 mL min⁻1 H2 flow, 53
ε-Poly-L-lysine (ε-PL), a broad-spectrum and efficient preservative, is widely used in food and pharmaceutical industries. In this study, the construction of engineered Streptomyces albulus by increasing ATP and NADH supply was carried out. Initially, the engineered strain BP3 was constructed by overexpressing pncB, pck, and pdh genes in S. albulus FL21. At 72h, both ATP and NADH levels in BP3 significantly increased compared to the control strain, while NADH/NAD ratio decreased. Consequently, ε-PL production by BP3 reached 1.61 g/L, representing a 30.89 Overexpression of pncB, pck and pdh enhanced ATP and NADH contents. The ε-PL production of BP3 increased by 30.89
