The metric of a spacetime can be greatly simplified if the spacetime is circular. We prove that in generic effective theories of gravity, the spacetime of a stationary, axisymmetric, and ...asymptotically flat solution must be circular if the solution can be obtained perturbatively from a solution in the general relativity limit. This result applies to a broad class of gravitational theories that include arbitrary scalars and vectors in their light sector, so long as their nonstandard kinetic terms and nonmininal couplings to gravity are treated perturbatively.
Allelopathy is an ecological phenomenon in which organisms interfere with each other. As a management strategy in agricultural systems, allelopathy can be mainly used to control weeds, resist pests, ...and disease and improve the interaction of soil nutrition and microorganisms. Volatile organic compounds (VOCs) are allelochemicals volatilized from plants and have been widely demonstrated to have different ecological functions. This review provides the recent advance in the allelopathic effects of VOCs on plants, such as growth, competition, dormancy, resistance of diseases and insect pests, content of reactive oxygen species (ROS), enzyme activity, respiration, and photosynthesis. VOCs also participate in plant-to-plant communication as a signaling substance. The main methods of collection and identification of VOCs are briefly summarized in this article. It also points out the disadvantages of VOCs and suggests potential directions to enhance research and solve mysteries in this emerging area. It is necessary to study the allelopathic mechanisms of plant VOCs so as to provide a theoretical basis for VOC applications. In conclusion, allelopathy of VOCs released by plants is a more economical, environmentally friendly, and effective measure to develop substantial agricultural industry by using the allelopathic effects of plant natural products.
With the implementation of new domestic garbage classification policy in China, attention is growing to improve the treatment efficiency of municipal ‘wet’ waste. Combing with the new regulation, the ...synergistic strategy and the microbial ecology of the anaerobic co-digestion (AcoD) of cooked food waste (CFW), uncooked food waste (UCFW) and rice straw (RS) were analyzed in current study. Results showed that the maximum cumulative methane yield (CMY) and synergic index were obtained when CFW and UCFW were mixed at the ratio of 1:1 (based on volatile solid content). The highest CMY 452.94 ± 0.99 mL/g-VS was obtained when the ratio of CFW, UCFW and RS was 0.81:0.09:0.10, which was 16.29%, 36.20% and 121.84% higher than their mono-digestion, respectively. The AcoD promoted the methane potential by prolonging the release time of organic matter and slowing down the hydrolysis rate. Furthermore, the AcoD increased the species diversification and relative abundance of fermentation bacteria in digesters, and Methanosaeta predominated the methanogen communities. This study demonstrated a clean and sustainable AcoD strategy for safe disposal of urban food waste and revealed the variation of microbial community, which can provide a base for efficient bioenergy recovery from urban domestic garbage.
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•The optimum mixing ratio for anaerobic co-digestion (AcoD) of CFW, UCFW and RS was 0.81:0.09:0.10.•AcoD prolonged the release of organic matter and slowed down the hydrolysis rate.•AcoD resulted in more diverse and abundant fermentation bacteria community.•Methanosaeta predominated the methanogen communities in AcoD of CFW, UCFW and RS.
Type-II multiferroic materials, in which ferroelectric polarization is induced by inversion nonsymmetric magnetic order, promise new and highly efficient multifunctional applications based on the ...mutual control of magnetic and electric properties. Although this phenomenon has to date been limited to low temperatures, here we report a giant pressure dependence of the multiferroic critical temperature in CuBr_{2}. At 4.5 GPa, T_{C} is enhanced from 73.5 to 162 K, to our knowledge the highest value yet reported for a nonoxide type-II multiferroic. This growth shows no sign of saturating and the dielectric loss remains small under these high pressures. We establish the structure under pressure and demonstrate a 60% increase in the two-magnon Raman energy scale up to 3.6 GPa. First-principles structural and magnetic energy calculations provide a quantitative explanation in terms of dramatically pressure-enhanced interactions between CuBr_{2} chains. These large, pressure-tuned magnetic interactions motivate structural control in cuprous halides as a route to applied high-temperature multiferroicity.
A key issue in layered materials is the dependence of their properties on their chemical composition and crystal structure in addition to the dimensionality. For instance, atomically thin magnetic ...structures exhibit novel spin properties that do not exist in the bulk. We use first-principles calculations, based on density functional theory, and machine learning to study the magnetocrystalline anisotropy of a set of single-layer two-dimensional structures that are derived from changing the chemical composition of the ferromagnetic semiconductor Cr2Ge2Te6. We discuss trends and identify descriptors for the magnetocrystalline anisotropy in monolayers with the chemical formula A2B2X6. Our data-driven study aims to provide physical insights into the microscopic origins of magnetic anisotropy in two dimensions. For instance, we demonstrate that hybridization plays a key role in determining the magnetic anisotropy of the materials investigated in this study. In addition, we demonstrate that first-principles calculations can be combined with machine learning to create a high-throughput computational approach for the targeted design of quantum materials with potential applications in areas ranging from sensing to data storage.
Two-dimensional (2D) layered materials offer intriguing possibilities for novel physics and applications. Before any attempt at exploring the materials space in a systematic fashion, or combining ...insights from theory, computation, and experiment, a formal description of information about an assembly of arbitrary composition is required. Here, we introduce a domain-generic notation that is used to describe the space of 2D layered materials from monolayers to twisted assemblies of arbitrary composition, existent or not yet fabricated. The notation corresponds to a theoretical materials concept of stepwise assembly of layered structures using a sequence of rotation, vertical stacking, and other operations on individual 2D layers. Its scope is demonstrated with a number of example structures using common single-layer materials as building blocks. This work overall aims to contribute to the systematic codification, capture, and transfer of materials knowledge in the area of 2D layered materials.
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