摘要 : We use the first-principle method to investigate the crystal structure, electronic structure, and magnetic properties of a Mn-doped MoSe2 monolayer (Mo0.75Mn0.25Se2). The spin-up electrons exhibit metallic properties, whereas the spin-down electrons exhibit insulating properties, indicating the half-metallic properties of Mo0.75Mn0.25Se2. The density of states shows a strong coupling between dopant Mn 3d orbitals via the Mo 4d and Se 4p states. We investigate the dispersion relation of the spin-spiral energy E(q) and the wave vector q for Mo0.75Mn0.25Se2 under the generalized Bloch condition. The exchange coupling coefficient Ji (i = 1, 2, 3, and 4) is obtained using the Heisenberg interaction model. The next-nearest-neighbor interaction exchange coupling coefficient J2 is non-negligible, although the first nearest neighbor, J1, plays the most important role in the interaction between atoms. Because Mo0.75Mn0.25Se2 is a two-dimensional (2D) metal material that can easily undergo oxidation, we use insulating MoSe2 to fabricate a MoSe2/Mo0.75Mn0.25Se2/MoSe2 heterostructure. First-principle calculations results show that the half-metallic ferromagnetic properties of Mo0.75Mn0.25Se2 can be protected very well in the heterostructure. The findings of this study can promote the understanding of the mechanism of 2D half-metallic ferromagnetic properties and provide a general method for designing materials that show such properties with stability. © 2022 Chinese Academy of Sciences. All rights reserved.

摘要 : Compared with the Hamiltonian mechanics and the Lagrangian mechanics, the Birkhoffian mechanics is more general. The Birkhoffian mechanics is discussed on the basis of the generalized fractional operators, which are proposed recently. Therefore, differential equations of motion within generalized fractional operators are established. Then, in order to find the solutions to the differential equations, Noether symmetry, conserved quantity, perturbation to Noether symmetry and adiabatic invariant are investigated. In the end, two applications are given to illustrate the methods and results.

摘要 : In this paper, we first give a new proof of the log-Minkowski inequality of general planar convex bodies and then extend the $$L_p$$ -Brunn–Minkowski inequality and $$L_p$$ -Minkowski inequality of o-symmetric planar convex bodies for $$p\in (0,1)$$ to $$\phi $$ -Brunn–Minkowski inequality and $$\phi $$ -Minkowski inequality of general planar convex bodies. As an application, a family of $$\phi $$ -measures of asymmetry for planar convex bodies is introduced.

摘要 : We focus on Mei symmetry for time scales nonshifted mechanical systems within Lagrangian framework and its resulting new conserved quantities. Firstly, the dynamic equations of time scales nonshifted holonomic systems and time scales nonshifted nonholonomic systems are derived from the generalized Hamilton's principle. Secondly, the definitions of Mei symmetry on time scales are given and its criterions are deduced. Finally, Mei's symmetry theorems for time scales nonshifted holonomic conservative systems, time scales nonshifted holonomic nonconservative systems and time scales nonshifted nonholonomic systems are established and proved, and new conserved quantities of above systems are obtained. Results are illustrated with two examples.

摘要 : GPS has a sharp performance decline in terms of accuracy indoors due to the complex building structure. A combined algorithm, targeting at received signal strength indication (RSSI) calibration optimisation, depending on deep neural network training via input vector Γ and the target output vector Ψ, termed reference signal optimisation algorithm (RSOA) is proposed to improve the positioning accuracy in the indoor Bluetooth positioning networks. Experimental results show that the relative error of the proposed RSOA between the estimated results and the measured ones can reach as low as 0.2%, and the absolute errors can be reduced to 0.13 m at most within 10 m.

摘要 : Hydrogel adhesives have been widely used in wet environments. Nonetheless, strong and stable persistent adhesion remains a challenge. Here, we report a facile yet powerful strategy to construct high-strength hydrogel adhesives for durable adhesion in a saline environment. Such a hydrogel consists of two polymer networks: a hydrophobic-associated polyacrylamide network of covalent and noncovalent cross-links and an alginate network cross-linked by divalent cations in saline. Meanwhile, polydopamine nanoparticles formed through in-situ self-polymerization are distributed evenly throughout the system to provide underwater adhesion. A low and controllable swelling rate and high compressive strength of hydrogels can be achieved via this multiple interaction strategy. Ultimately, this strategy contributes to the persistent underwater adhesion of hydrogels, and the decreasing rate of lap-shear adhesion strength of hydrogels is only 24.79 ± 8.01% after saline immersion for up to 21 days. Moreover, good cytocompatibility of hydrogels is helpful for their application in the biomedical field.

摘要 : Background.Polychlorinated biphenyls (PCBs) are synthetic and persistent toxic chemicals with a high potential to bioaccumulate in human tissue. There is no existing literature on workers' perceptions and occupational cancer risk due to exposure to PCBs in Ethiopia.Objectives.The aim of the present study was to assess workers' perceptions of occupational health and safety measures of PCB management and to evaluate the cancer risk posed by PCBs to workers handling these chemicals in Ethiopia.Methods.A total of 264 questionnaires were administered to workers at the study area to obtain information about PCB management. A mathematical model adopted from the United States Environmental Protection Agency (USEPA) was used to assess the potential cancer risk of people working in PCB-contaminated areas.Results.The results showed that the majority of the workers had little knowledge of safe PCB management practices. Furthermore, 82.6% had not received training on chemical management and occupational health and safety protocols. The association between respondents' responses on the impact of PCBs to the use of personal protective equipment was statistically significant (p <0.005). Accidental ingestion, dermal contact and inhalation exposure pathways were considered in assessing the cancer risk of people working in these areas. The estimated cancer risk for PCBs via dermal contact was higher than for the accidental ingestion and inhalation pathways. The health risk associated with dermal contact was 73.8-times higher than the inhalation exposure route. Workers at the oil tanker and oil barrel area and swampy site are at higher risk of cancer via dermal contact at the 95th centile (879 and 2316 workers per million due to PCB exposure, respectively). However, there is very low cancer risk at the staff residence and garden area via the inhalation route.Conclusions.Training programs would help improve the knowledge of workers in the area of occupational health and safety of chemical handling. Further studies on PCBs in the exposed workers will provide information on their blood sera PCB levels and consequently identify potential health impacts.Participant Consent.ObtainedEthics Approval.Ethics approval was obtained from the Research Ethics Review Committee of Adama Hospital Medical College, Adama, Ethiopia.Competing Interests.The authors declare no competing financial interests.

摘要 : UV induced decomposition of perovskite material is one of the main factors to severely destroy perovskite solar cells for instability. Here we report a UV stable perovskite solar cell with an Fe2O3 electron transport layer (ETL) made by spin-coating water dispersed Fe3O4 nanoparticles. Devices with Fe2O3 ETLs prepared from 10 nm Fe3O4 nanoparticles show nearly no decrease of photoelectric conversion efficiency (PCE) upon continuous exposure to very high UV light irradiation (300 W Xe lamp) for 10 hours in contrast to the TiO2 ETL based samples with more than 30% reduction of PCE, and their PCE (14.33) is also much superior to those of devices with Fe2O3 ETLs made conventionally from FeCl3 solution (7.7%). Through the study of Fe2O3 thin film prepared perovskite solar cells, it is found that compact, high transmittance, low leakage and low transmission impedance devices can be obtained by using an appropriate size of Fe3O4 nanoparticles. Our major findings are expected to provide a guide to design UV-protected compact electron transport layers for UV-stable perovskite solar cells.

摘要 : In traditional settlements in Southwest China, there are many timber historical buildings and residential buildings, which feature a low fire resistance rating. The preservation and inheritance of these timber buildings are mainly threatened by fire. However, the existing research has not explored the deep correlation between the spatial structure of settlements and fire. To make up for the gap, this paper aims to find the ideas and measures that effectively prevent the fire from occurring in timber buildings of traditional settlements in Southwest China, based on fractal and seepage theory. Firstly, the fractal features were extracted from the spatial structure of these settlements. Then, the authors identified the factors affecting the spread of fire in buildings, and analyzed the mechanism of fire propagation between the timber buildings of traditional settlements. On this basis, a fire prevention scheme was proposed, which integrates the "targeted control of overall structure" with "comprehensive synergy between multiple local elements". The research results provide a reference for applying fractal and seepage theory in the fire prevention of other buildings with special structures.

摘要 : By random growth method, this paper constructs isotropic porous media, anisotropic-1 porous media, and anisotropic-2 porous media, which have the same porosity but different micropore morphologies, and explores how the pore morphology affects the water vapor diffusion in the pores of porous media. The results show that: the random growth method can effectively reconstruct various porous moisture conditioning materials, and control their porosity and pore morphology; the equilibrium water vapor concentration and stabilization time of water vapor diffusion can effectively demonstrate the pore connectivity of porous media and the dynamic migration features of materials in the pores; the greater the change in the equilibrium water vapor concentration, the faster the stabilization of water vapor diffusion, and the better the pore connectivity of porous media.