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Double Majorana vortex flat bands in the topological Dirac superconductor
No full textVortex lines, known as topological defects, are capable of trapping Majorana modes in superconducting topological materials. Previous studies have primarily focused on topological bands with conventional s-wave pairing. However, topological Dirac semimetals exhibiting a unique orbital texture can favor unconventional pairing when electronic correlations are significant. The topology of vortices in these systems remains elusive and unexplored. In this work, we investigate the vortex bound states in C4z-symmetric superconducting Dirac semimetals, with a particular focus on the orbital-singlet unconventional pairing, which generates higher-order Majorana hinge modes. We identify robust doubly-degenerate Majorana vortex flat bands at zero energy in both type-I and type-II Dirac semimetals. These doubly-degenerate flat bands arise from a nontrivial Z2 topology defined by an effective particle-hole symmetry and are protected by the four-fold rotational symmetry. Additionally, we observe that moving the vortex line close to a hinge can trivialize the higher-order Majorana arc on the hinge, leaving a single Majorana mode at the vortex core due to the hybridization of Majorana modes. Finally, we discuss the potential experimental implications for correlated Dirac semimetals, such as electron-doped iron-based superconductors.</p
The shocks matter: labor mobility and the welfare cost of a currency union
No full textIn this paper, we study the impact of labor mobility on the welfare cost of a currency union in an open economy New Keynesian model. We find that the relationship between labor mobility and exchange rate flexibility depends on the source of asymmetric regional shocks. With demand shocks, labor mobility reduces the welfare cost of a union by reducing the cost of shifting labor to concentrated areas of high demand. With supply shocks, flexible exchange rates can work in conjunction with higher labor mobility to reallocate the factors of production to higher productivity regions of potential currency areas. Therefore, higher labor mobility can widen the welfare gap between fixed and flexible exchange rate regimes, implying areas with high inter-regional labor mobility may benefit more from exchange rate flexibility.</p
A peridynamics-based topology optimization framework for enhancing dynamic fracture resistance
No full textDynamic fracture in brittle and quasi-brittle structures under impact or blast loading presents a critical design challenge where enhanced fracture resistance is essential for safety. While topology optimization (TO) offers a powerful approach for systematic design, its application to dynamic fracture problems remains largely unexplored due to the complexities of rate effects, inertia, and crack propagation. This study introduces a novel TO framework that integrates bond-based peridynamics—a nonlocal theory adept at modeling dynamic crack initiation and propagation—with gradient-based TO methods to design structures with superior fracture resistance under dynamic loading. We formulate a fracture-driven multi-objective function that simultaneously maximizes total fracture energy (toughness), penalizes early-time fracture energy (delaying crack initiation), and preserves structural stiffness under a volume constraint. The analytical sensitivities for this dynamic problem are rigorously derived using an adjoint method. To enable efficient, large-scale computation, an OpenCL-based parallel acceleration scheme is implemented. The framework is validated on two benchmark problems: an L-shaped panel and a pre-cracked cantilever beam. Compared to stiffness-maximized designs, our optimized structures achieve two- to threefold increases in fracture toughness and delay crack initiation by 12 %–31 %, while maintaining comparable stiffness. We further demonstrate that optimal topologies are highly loading-rate-specific, underscoring the necessity of a dynamic fracture perspective in design. The proposed framework provides a physically consistent and computationally efficient pathway for designing fracture-resistant structures under dynamic conditions.</p
MSfusion: A Dynamic Model Splitting Approach for Resource-Constrained Machines to Collaboratively Train Larger Models
No full textTraining large models requires a large amount of data, as well as abundant computation resources. While collaborative learning provides a promising paradigm to harness collective data from many participants, training large models remains a major challenge for participants with limited resources. We introduce MSfusion, an effective and efficient collaborative learning framework, tailored for training larger models on resource-constraint machines through model splitting. Specifically, a double shifting model splitting scheme is designed. Each participant is assigned a subset of model parameters to train over local data, and aggregates with sub-models of other peers on common parameters. While model splitting significantly reduces the computation and communication costs of individual participants, additional novel designs on adaptive model overlapping and contrastive loss functions help MSfusion to maintain training effectiveness, against model shift across participants. Extensive experiments on image and NLP tasks illustrate significant advantages of MSfusion in performance and efficiency for training large models, and its strong scalability: computation cost of each participant reduces significantly as the number of participants increases.</p
Local charge redistribution-induced OER mechanism switching in RuO<sub>2</sub>-based catalysts for efficient PEM electrolysis
No full textOxygen evolution reaction (OER) is widely recognized as a bottleneck of water electrolysis. To determine the underlying reaction mechanisms, particularly the relative contribution of the adsorbate evolution mechanism (AEM) and lattice-oxygen participation mechanism (LOM), we conduct a comprehensive investigation combining Density Functional Theory (DFT) calculations and experimental validation. Our theoretical analysis of doped RuO2 catalysts reveals that heteroatom doping (Ni, Cu, and Zn) induces significant local charge transfer, leading to the increased charge state of Ru and the downshifted d-band center. This, in turn, enables the mechanism switching from the conventional AEM to the more efficient LOM, and finally improves OER activity. We also establish a simple yet powerful descriptor, Ne of Ru (representing charge density of Ru sites), which enables accurate prediction of both catalytic activity and stability. Guided by these theoretical predictions, we successfully synthesize a Ni-doped RuO2 catalyst, which exhibits excellent OER activity and stability in acidic media, achieving an overpotential of just 156 mV and maintaining stability for 4000 h at 10 mA cm−2, significantly surpassing the performance of the commercial RuO2. These findings not only provide fundamental insights into the mechanism-switching behavior in OER catalysis but also offer a practical strategy for designing high-performance, stable electrocatalysts for acidic water electrolysis.</p
Ultra-stable and large elastocaloric effect in a nano-precipitated bulk TiNiCuCo shape memory alloy
No full textElastocaloric cooling utilizes the latent heat of shape memory alloys (SMAs) during cyclic phase transition and has emerged as an environmentally-friendly technology. However, existing SMAs exhibit either unsatisfactory cyclic stability or insufficient adiabatic temperature drop (ΔT), constraining the development of this technology. Here, we develop a nano-precipitated bulk TiNiCuCo SMA which retains a stable and large ΔT of 17 K over 1 × 108 phase-transition cycles. The large ΔT originates from the large entropy change of B2-B19′ phase transition in the Cu-lean B2 matrix. The ultra-high cyclic stability is realized by inhibiting dislocation motion via precipitation hardening of uniformly distributed Ti(Ni,Cu)2 nanoprecipitates. Our nano-precipitated bulk TiNiCuCo demonstrates high competitiveness among existing SMAs, serving as a cornerstone for the development of high-performance elastocaloric cooling devices.</p
Phosphorus recovery from wastewater using waste gypsum via sulfur-metabolizing bacteria: Influence of gypsum type on performance and mechanisms
No full textWith global phosphorus depletion, a novel strategy for phosphorus recovery from phosphorus-laden wastewater combined with phosphogypsum recycling to form hydroxyapatite (Ca10(PO4)6(OH)2) via sulfur-metabolizing bacteria was recently developed. However, enhancing recovery efficiency and reducing costs in complex wastewater systems remain key challenges, primarily due to variations in binding energy and impurity species within waste-gypsum from different sources. Therefore, the effects of three waste gypsum types (phosphogypsum [PG], titanium gypsum [TG], and flue gas desulfurization gypsum [FGD]) on recovery efficiency and mechanisms were evaluated/elucidated, with analytical-grade CaSO4·2H2O (ARG) as the reference material. Results revealed that waste gypsum selection is pivotal for efficient phosphorus recovery in sulfur-metabolizing microbial systems. Although a negative correlation was observed between phosphorus recovery efficiency and gypsum stability (FGD > TG > PG > ARG), deviations from this trend occurred due to the specific impurity composition of the waste gypsum. TG, containing abundant Fe impurities, inhibited sulfur-metabolizing bacterial activity and impeded Ca-P precipitation. Despite intermediate stability, PG emerged as the optimal substrate, achieving 62.86 % phosphorus recovery efficiency. This superior performance was attributed to PG's phosphorus-containing impurity species, which actively promoted Ca-P formation (72 % proportion in sediments). Final economic evaluation demonstrated that utilizing PG as the treatment additive for wastewater phosphorus recovery achieved optimal waste gypsum valorization, delivering a net economic benefit of 0.89–1.30 per ton).</p
Three-dimensional management needs of deep-sea hydrothermal vent ecosystems
No full textDeep-sea hydrothermal vents form small, unique, and fragile ecosystems that are widely recognized as sites in need of protection. Deep-seabed mining (DSM) is a future threat to hydrothermal ecosystem integrity. In most areas within, and in all areas beyond national jurisdiction, currently proposed protection measures from DSM are unlikely to be sufficient, as only the known active venting sites on the seafloor are intended to be protected from DSM impacts. To ensure effective protection, we propose protecting not only the active vent sites but the entire hydrothermal ecosystems and their transition zones, embracing the seafloor, subseafloor and overlying water column. We discuss how ecological knowledge supports the proposed three-dimensional (3-D) protection. We suggest no DSM extraction or indirect impacts on the seafloor and entire subseafloor within a minimum 50 km diameter (25 km radius) around visible active vents. This will ensure the maintenance of subseafloor connections that are key for ecosystem integrity, as changes in vent fluid conditions can alter all ecosystem functions and services linked to venting activity. In the water column, protection from pollution from the seafloor to surface is suggested to protect vent larvae. This extent spans the entire length of ridges or back-arc basins, with a cross-axial extent of 80 km. We further discuss how international law can contribute to the effective protection of vent ecosystems and transition zones in international waters, and provide guidance for coastal States to safeguard these ecosystems and transition zones within their own maritime areas.</p
Boosting the Efficiency and Mechanical Stability of Organic Solar Cells Through a Polymer Acceptor by Reducing the Elastic Modulus
No full textOrganic solar cells (OSCs) are regarded as one of the most promising flexible power sources due to their lightweight and flexible properties, with the improvement of photovoltaic and mechanical performance. To improve the current density and power conversion efficiency (PCE), mPh4F-TS (TS) and PYSe2F-T (PA) are introduced into the binary host, PM6/mPh4F-TT (PM6/TT) as third components. It is demonstrated that the corresponding ternary devices, in both rigid and flexible devices, achieved superior efficiencies (19.6%/17.7% for PM6/TT+TS, and 19.2%/17.4% for PM6/TT+PA) outperform the binary counterparts (18.3%/16.4%). However, distinct differences in mechanical performance are observed between the polymer acceptor (PA) and small-molecular acceptor (TS). The PM6/TT+PA significantly improved the mechanical stability of flexible devices with a lower elastic modulus of 3.6 GPa, while the PM6/TT+TS resulted in the opposite effect with a higher elastic modulus of 5.5 GPa. Through in-depth investigation, a clear correlation between the elastic modulus, crack density, and mechanical stability of the active layer blends is successfully established, revealing the key role of reducing the elastic modulus in enhancing the mechanical stability of flexible OSCs. This study provides important guidance for the development of flexible photovoltaic devices with both high efficiency and mechanical robustness.</p
Alginate-Sludge Derived Biochar-Calcium Hydrogel for Phosphate Removal and Slow-Release Fertilizer: A Sustainable and Multifunctional Solution
No full textPhosphorus (P) pollution and depletion pose significant environmental and agricultural challenges. In this study, a multifunctional alginate-biochar-calcium (ABC) hydrogel for efficient phosphate removal and slow-release fertilization is developed. The hydrogel is synthesized by pyrolyzing biological sewage sludge to produce biochar, followed by calcium chloride modification and cross-linking with sodium alginate. The ABC-hydrogel achieves a high phosphate adsorption capacity, with maximum adsorption of 252.15 mg g−1, and enables controlled phosphate release, with 48% gradually released over 37 days, supporting sustained plant growth. Pot experiments demonstrate its agricultural benefits, with the P-loaded hydrogel enhancing the wet weight of lettuce by 110% compared to the control group. Additionally, the treatment methods, including pyrolysis, calcium modification, and crosslinking in hydrogel, significantly reduce the ecological risk of heavy metals in biological sewage sludge, lowering the ecological risk index (ERI) from 533.13 to 5.79, effectively transforming sludge from waste into a safe and valuable resource for agricultural and environmental applications. With a water absorption capacity of 439.22%, the hydrogel improves soil moisture retention, making it particularly beneficial for drought-prone regions. This work significantly contributes to sustainable phosphorus management by converting waste sludge into a valuable resource, offering promising applications in agriculture, phosphate removal, and waste reutilization.</p