National Science Review最新文献

The integration of high-temperature superconductors into electric propulsion systems, particularly applied-field magnetoplasmadynamic thrusters (AF-MPDTs), has recently garnered significant attention. However, research on low-power, high-temperature-superconducting (HTS)-based MPDTs, which are crucial for small satellites and CubeSats, remains limited. The increasing demand for compact, high-efficiency propulsion in low Earth orbit underscores the need for scalable HTS-AF-MPDT systems operating below 15 kW. Despite this, challenges such as the lack of detailed theoretical models, limited plasma diagnostics and excessive Joule heating in conventional copper magnets persist. In this work, using a downscaled version of a 25 kW HTS-based AF-MPDT, we address these limitations by developing and experimentally validating a theoretical MHD-based plasma-acceleration model for an AF-MPDT equipped with a conduction-cooled HTS magnet. The system achieves a specific impulse of 3265 s at an input power of 12 kW, more than eight times higher than traditional chemical propulsion, alongside a thrust of 320 mN and an efficiency of 25% at sub-12 kW. The HTS magnet reduces magnetic power consumption from 285 kW to under 1 kW and lowers magnet mass from 220 to 60 kg, enabling substantial improvements in system miniaturization and efficiency. These results represent the first reported demonstration of a 12 kW HTS AF-MPDT, bridging theoretical predictions with experimental outcomes and laying the groundwork for in-orbit demonstration of high-performance propulsion for small satellites.

Upper-layer ozone (O₃) intrusion (ULOI) is an important source of surface O₃, affecting gas pollutants and secondary aerosol formation. However, no robust method has been reported to identify ULOI events based on ground observations and assess their effects on surface atmospheric chemistry. We propose a novel method to identify ULOI events by ranking O₃ concentrations before dawn and evaluate their contributions to ground-level O₃ and aerosol formation across China. Our results show that ULOI events occur at a rate of 22%-74% across China, with higher frequency in eastern and southern coastal regions. ULOI enhances ground-level O₃ by 13-43 ppbv at night and 3-14 ppbv during the day. This increases atmospheric oxidation capacity (AOC) and enhances the contribution of the O₃ oxidation path to sulfate and secondary organic aerosol (SOA) formation. This study emphasizes the importance of atmospheric layer interactions and the impact of ULOI events on surface atmospheric chemistry.

The sources and mechanisms driving fluxes of dissolved gaseous mercury (DGM) in aquatic ecosystems represent a critical yet poorly constrained component of the global mercury (Hg) cycle. Current models assume that DGM is primarily formed through the reduction of Hg^II in water, largely supplied by atmospheric Hg^II deposition. Here we quantify the Δ²⁰⁰Hg signatures of DGM across marine (median: 0.02‰) and freshwater (0.02‰) ecosystems, intermediate between water dissolved Hg^II and atmospheric Hg⁰. This indicates that DGM in natural waters is not derived solely from Hg^II reduction as previous assumed but also from atmospheric input of Hg⁰ during air-sea gas exchange. A Δ²⁰⁰Hg-based mixing model reveals that ∼40% and 54% of DGM in seawater and freshwater, respectively, is derived directly from atmospheric Hg⁰ input. Combining these findings with an existing oceanic Hg budget, we show that re-emission of previously deposited atmospheric Hg⁰ accounts for ∼70% of gross oceanic Hg⁰ evasion. Consequently, we demonstrate that existing models have systematically underestimated gross atmospheric Hg⁰ deposition while overestimating net oceanic Hg⁰ emissions.

The advancement of all-solid-state lithium batteries (ASSLBs) requires innovative breakthroughs in catholyte design to eliminate the need for external pressure and mitigate the adverse effects of inactive catholytes on energy density. Here, we present a capacity-expanding O/Cl-bridged catholyte (1.2LiOH-FeCl₃) featuring an abundant, freely rotating Fe_xO_yCl_z framework, endowing it with polymer-like viscoelasticity and an impressive ionic conductivity (6.1 mS cm^-1 at 25°C). The polymer-like viscoelasticity creates a soft interface that alleviates volume changes during cycling, enabling zero-pressure ASSLBs to deliver a high capacity retention of 86.6% after 100 cycles, which is a 35.7% improvement compared to the rigid Li₂ZrCl₆ catholyte (50.9%). Moreover, the fast Li⁺ transport capability and variable-valence iron coordination center endow 1.2LiOH-FeCl₃ catholyte delivering a capacity of 97.7 mAh g^-1. When used as a catholyte alongside an LiFePO₄ (LFP) cathode material, it increases capacity by 31.3% (196.4 vs. 149.6 mAh g^-1 _LFP) and boosts energy density by 21.1% (609.4 vs. 503.4 Wh kg^-1 _LFP) compared to Li₂ZrCl₆ catholyte. Beyond these properties, the 1.2LiOH-FeCl₃ catholyte offers significant cost advantages, priced at just $2.6 kg^-1 (16% of the cost of Li₂ZrCl₆), and supports scalable production at 60°C, making kilogram- to ton-level manufacturing feasible.

How to manage the compounding risks to national food security is a major issue of global concern. China, as the world's largest producer of staple foods, has steadily strengthened its food security level, profoundly impacting global food systems. In this review, we propose a systemic resilience framework (the ability to predict, absorb, rebound from and adapt to disruptions) to analyze the evolution of China's food security and explore its driving factors and multidimensional adaptations. China's food security resilience has progressed through three distinct stages: low resilience (achieving basic sufficiency), medium resilience (achieving nutritional adequacy) and above-medium resilience (embracing sustainability). Multidimensional synergistic adaptation-integrating agricultural, climatic, socioeconomic and land-use strategies-has been key to these achievements. While agricultural advancements have significantly bolstered China's food security, the growing pressures of climate change threaten to undermine these achievements. We project that China's staple food self-sufficiency will remain above 98%, yet the overall food balance is expected to tighten under the combined pressures of dietary shifts and resource constraints. To better enhance the systemic resilience in China's food security, China can buffer climate- and water-related shocks by expanding high-standard farmland, ease resource and demand pressures by enforcing anti-food-waste laws, strengthen soil and water resilience through nature-based solutions, and dampen trade volatility with integrated climate-market early-warning systems. Insights from China's experience provide targeted levers for enhancing food-system resilience elsewhere.

As a consequence of the evolution of the water-bearing basal magma ocean, water-induced mantle overturn can suitably explain many puzzling observations in the Archean, including the formation of continents and the Archean-Proterozoic boundary. The upwelling of the hot basal magma ocean during mantle overturn drastically affects the thermal state of the core-mantle boundary and geomagnetic field. We model the thermal evolution of the core-mantle boundary to investigate the effects of mantle overturn on the geomagnetic field. Our results demonstrate that mantle overturn substantially accelerates core cooling and increases heat flow across the core-mantle boundary. Such enhanced heat flow would have strengthened the geomagnetic field, which explains well the high paleointensity records from ∼3.5 to 2.5 Ga. The strong geodynamo and formation of Archean continents generate a concordant picture of the evolution of water-induced mantle overturn.

Universal grasping is essential but challenging in robotic manipulations, particularly for humanoid robots with multifingered hands. To learn skills of dexterous manipulations from humans, we propose a sensory-control synergy (SCS) approach mimicking the human grasping experience. We develop a tactile glove worn on a human hand to capture multimodal tactile data (contact, slip and pressure) during human grasping demonstrations. Emulating human neurocognition, the multimodal tactile data are encoded into semantically explicit grasping states by neural-network computing. Drawing on human motor control strategies, an experience-based fuzzy controller is built to swiftly convert semantic grasping states into grasping actions. Benefiting from the semantization of grasping states, the SCS model is highly logicalized and generalizable, can be data-efficiently built by non-experts and readily transferred to robots for accomplishing universal robotic manipulation. The robot with SCS achieves an average success rate of 95.2% in grasping diverse objects of daily life, including slippery, fragile, soft and heavy objects. In dynamic disturbance and complex tasks, the robot autonomously manipulates using its adaptive SCS, demonstrating human-like universal grasping capabilities.