We investigate the shadows and photon spheres of the four-dimensional Gauss–Bonnet black hole with the static and infalling spherical accretions. We show that, for both cases, there always exist ...shadows and photon spheres. The radii of the shadows and photon spheres are independent of the profiles of accretion for a fixed Gauss–Bonnet constant, implying that the shadow is a signature of the spacetime geometry and it is hardly influenced by accretion. Because of the Doppler effect, the shadows of the infalling accretion are found to be darker than in the static case. We also investigate the effect of the Gauss–Bonnet constant on the shadow and photon spheres, and we find that the larger the Gauss–Bonnet constant is, the smaller the radii of the shadow and photon spheres will be. In particular, the observed specific intensity increases as the Gauss–Bonnet constant grows.
We investigate the effects of quintessence dark energy on the shadows of black hole, surrounded by various profiles of accretions. For the thin-disk accretion, the images of the black hole comprises ...the dark region and bright region, including direct emission, lensing rings and photon rings. Although their details depend on the form of the emission, generically, direct emission plays a major role for the observed brightness of the black hole, while the lensing ring makes a small contribution and the photon ring makes a negligible contribution. The existence of a cosmological horizon also plays an important role in the shadows, since the observer in the domain of outer communications is near the cosmological horizon. For spherically symmetric accretion, static and infalling matters are considered. We find that the positions of photon spheres are the same for both static and infalling accretions. However, the observed specific intensity of the image for infalling accretion is darker than for static accretion, due to the Doppler effect of the infalling motion.
Fundamental understanding of the dependence between the structure and composition on the electrochemical CO2 reduction reaction (CO2RR) would guide the rational design of highly efficient and ...selective electrocatalysts. A major impediment to the deep reduction CO2 to multi‐carbon products is the complexity of carbon–carbon bond coupling. The chemically well‐defined catalysts with atomically dispersed dual‐metal sites are required for these C−C coupling involved processes. Here, we developed a catalyst (BIF‐102NSs) that features Cl− bridged dimer copper (Cu2) units, which delivers high catalytic activity and selectivity for C2H4. Mechanistic investigation verifies that neighboring Cu monomers not only perform as regulator for varying the reaction barrier, but also afford distinct reaction paths compared with isolated monomers, resulting in greatly improved electroreduction performance for CO2.
Chemically well‐defined catalysts with atomically dispersed dimer‐copper sites are elaborated to modulate the reaction path of CO2 electroreduction reaction (CO2RR). The BIF‐102NSs catalyst with Cl− bridged dimer copper (Cu2) units shows higher catalytic activity and selectivity for C2H4, because the neighboring Cu monomers perform as regulator for varying the reaction barrier and afford distinct reaction paths compared with isolated monomers.
The anomalous Hall effect is a fundamental transport process in solids arising from the spin-orbit coupling. In a quantum anomalous Hall insulator, spontaneous magnetic moments and spin-orbit ...coupling combine to give rise to a topologically nontrivial electronic structure, leading to the quantized Hall effect without an external magnetic field. Based on first-principles calculations, we predict that the tetradymite semiconductors Bi₂Te₃, Bi₂Se₃, and Sb₂Te₃ form magnetically ordered insulators when doped with transition metal elements (Cr or Fe), in contrast to conventional dilute magnetic semiconductors where free carriers are necessary to mediate the magnetic coupling. In two-dimensional thin films, this magnetic order gives rise to a topological electronic structure characterized by a finite Chern number, with the Hall conductance quantized in units of e²/h (where e is the charge of an electron and h is Planck's constant).
Photocatalytic reduction of CO2 to value‐added fuel has been considered to be a promising strategy to reduce global warming and shortage of energy. Rational design and synthesis of catalysts to ...maximumly expose the active sites is the key to activate CO2 molecules and determine the reaction selectivity. Herein, we synthesize a well‐defined copper‐based boron imidazolate cage (BIF‐29) with six exposed mononuclear copper centers for the photocatalytic reduction of CO2. Theoretical calculations show a single Cu site including weak coordinated water delivers a new state in the conduction band near the Fermi level and stabilizes the *COOH intermediate. Steady‐state and time‐resolved fluorescence spectra show these Cu sites promote the separation of electron–hole pairs and electron transfer. As a result, the cage achieves solar‐driven reduction of CO2 to CO with an evolution rate of 3334 μmol g−1 h−1 and a high selectivity of 82.6 %.
The cat on the cage: A copper‐based boron imidazolate cage with isolated, coordinatively unsaturated single copper atom active sites was found to be as an excellent co‐catalyst for highly efficient and selective solar‐driven CO2 reduction to CO.
In this brief, we incorporate the impact of preferential imitation rule into a vaccination game based epidemic spreading model on social networks, where each individual chooses one of its neighbors ...as an imitation reference with a probability proportional to the neighbor's degree. Our results indicate that the vaccination coverage can be remarkably increased if hub nodes are preferentially imitated, leading to the dramatic reduction of the epidemic size. We explain this by suggesting that the vaccination willingness of hub nodes is very high when voluntary vaccination mechanism is assumed, who can attract more individuals to take vaccination if they are preferentially imitated. Moreover, a mean-field theoretical approach is developed to further verify our findings. This brief suggests that the human behavioral response is an important factor for spreading dynamics.
Nanostructuring of magnetically hard and soft materials is fascinating for exploring next‐generation ultrastrong permanent magnets with less expensive rare‐earth elements. However, the resulting ...hard/soft nanocomposites often exhibit random crystallographic orientations and monomorphological equiaxed grains, leading to inferior magnetic performances compared to corresponding pure rare‐earth magnets. This study describes the first fabrication of a novel bimorphological anisotropic bulk nanocomposite using a multistep deformation approach, which consists of oriented hard‐phase SmCo rod‐shaped grains and soft‐phase Fe(Co) equiaxed grains with a high fraction (≈28 wt%) and small size (≈10 nm). The nanocomposite exhibits a record‐high energy product (28 MGOe) for this class of bulk materials with less rare‐earth elements and outperforms, for the first time, the corresponding pure rare‐earth magnet with 58% enhancement in energy product. These findings open up the door to moving from a pure permanent‐magnet system to a stronger nanocomposite system at lower costs.
The fabrication of novel bimorphological anisotropic SmCo7/Fe(Co) bulk nanostructures with a multistep deformation approach is demonstrated. The structures exhibit a record‐high energy product (28 MGOe) for this class of bulk materials with less rare‐earth elements. The resulting nanocomposite outperforms, for the first time, a corresponding pure rare‐earth permanent magnet (SmCo7) with 58% enhancement in energy product.
Although seagrasses and marine macroalgae (macro‐autotrophs) play critical ecological roles in reef, lagoon, coastal and open‐water ecosystems, their response to ocean acidification (OA) and climate ...change is not well understood. In this review, we examine marine macro‐autotroph biochemistry and physiology relevant to their response to elevated dissolved inorganic carbon DIC, carbon dioxide CO₂, and lower carbonate CO₃ ²⁻ and pH. We also explore the effects of increasing temperature under climate change and the interactions of elevated temperature and CO₂. Finally, recommendations are made for future research based on this synthesis. A literature review of >100 species revealed that marine macro‐autotroph photosynthesis is overwhelmingly C₃ (≥ 85%) with most species capable of utilizing HCO₃ ⁻; however, most are not saturated at current ocean DIC. These results, and the presence of CO₂‐only users, lead us to conclude that photosynthetic and growth rates of marine macro‐autotrophs are likely to increase under elevated CO₂ similar to terrestrial C₃ species. In the tropics, many species live close to their thermal limits and will have to up‐regulate stress‐response systems to tolerate sublethal temperature exposures with climate change, whereas elevated CO₂ effects on thermal acclimation are unknown. Fundamental linkages between elevated CO₂ and temperature on photorespiration, enzyme systems, carbohydrate production, and calcification dictate the need to consider these two parameters simultaneously. Relevant to calcifiers, elevated CO₂ lowers net calcification and this effect is amplified by high temperature. Although the mechanisms are not clear, OA likely disrupts diffusion and transport systems of H⁺ and DIC. These fluxes control micro‐environments that promote calcification over dissolution and may be more important than CaCO₃ mineralogy in predicting macroalgal responses to OA. Calcareous macroalgae are highly vulnerable to OA, and it is likely that fleshy macroalgae will dominate in a higher CO₂ ocean; therefore, it is critical to elucidate the research gaps identified in this review.
Cyber-physical systems embed software into the physical world. They appear in a wide range of applications such as smart grids, robotics, and intelligent manufacturing. Cyber-physical systems have ...proved resistant to modeling due to their intrinsic complexity arising from the combination of physical and cyber components and the interaction between them. This study proposes a general framework for discovering cyber-physical systems directly from data. The framework involves the identification of physical systems as well as the inference of transition logics. It has been applied successfully to a number of real-world examples. The novel framework seeks to understand the underlying mechanism of cyber-physical systems as well as make predictions concerning their state trajectories based on the discovered models. Such information has been proven essential for the assessment of the performance of cyber-physical systems; it can potentially help debug in the implementation procedure and guide the redesign to achieve the required performance.
Mechanisms of soil organic carbon (SOC) stabilization have been widely studied due to their relevance in the global carbon cycle. No‐till (NT) has been frequently adopted to sequester SOC; however, ...limited information is available regarding whether sequestered SOC will be stabilized for long term. Thus, we reviewed the mechanisms affecting SOC stability in NT systems, including the priming effects (PE), molecular structure of SOC, aggregate protection, association with soil minerals, microbial properties, and environmental effects. Although a more steady‐state molecular structure of SOC is observed in NT compared with conventional tillage (CT), SOC stability may depend more on physical and chemical protection. On average, NT improves macro‐aggregation by 32.7%, and lowers SOC mineralization in macro‐aggregates compared with CT. Chemical protection is also important due to the direct adsorption of organic molecules and the enhancement of aggregation by soil minerals. Higher microbial activity in NT could also produce binding agents to promote aggregation and the formation of metal‐oxidant organic complexes. Thus, microbial residues could be stabilized in soils over the long term through their attachment to mineral surfaces and entrapment of aggregates under NT. On average, NT reduces SOC mineralization by 18.8% and PE intensities after fresh carbon inputs by 21.0% compared with CT (p < .05). Although higher temperature sensitivity (Q10) is observed in NT due to greater Q10 in macro‐aggregates, an increase of soil moisture regime in NT could potentially constrain the improvement of Q10. This review improves process‐based understanding of the physical and chemical mechanism of protection that can act, independently or interactively, to enhance SOC preservation. It is concluded that SOC sequestered in NT systems is likely to be stabilized over the long term.
Understanding the mechanisms of soil organic carbon (SOC) stability could be better to predict the SOC fate under climate change. Our review identified the factors affecting SOC stability and the roles of microbial residues in SOC stability regulated by physicochemical protection. This study provides systematic evidences of enhanced SOC accumulation under no‐till at upper soil depth, and improves process‐based understanding of the physical and chemical mechanisms of protection that can act, independently or interactively, to enhance SOC preservation. It is concluded that SOC sequestered in no‐till systems could be stabilized over the long term.
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