摘要 : As mankind steps into the 21st century, the exploration of the ocean also enters a new phase. In the recent decades, the research on biomimetic robot fish has attracted scientific communities' attention increasingly. With its character of high flexibility and intelligence, biomimetic robot fish have become one of the research focuses in the field of underwater robots in recent years. This paper mainly describes the classification of propulsion modes and the corresponding characteristics, the international research situation, the open problems and future research issues for biomimetic robot fish.

摘要 : The Afram Plains watershed is one of the major watersheds located at the lower part of the Volta Basin in Ghana with high groundwater usage. Dependency on groundwater is a fast-growing concern in the plains due to the unreliable supply of surface water. This has put the groundwater resources under intense pressure and has necessitated the need for sustainable management of the groundwater resources. This study aimed to estimate the recharge, spatial distribution, and potential recharge zones of groundwater at different scales in the Afram Plains area using the Soil and Water Assessment Tool (SWAT) model and Geography Information System (GIS) approach. The SWAT model was set up (1983–2016), calibrated (1983–1990) and validated (1991–1997) using digital elevation model, soil, land use, climate datasets, and discharge data. The GIS approach was used to produce thematic maps for eight contributing factors; rainfall, elevation, land cover land use, lineaments, drainage, geology, soil and slope for mapping the recharge zones. The results showed that about 1.65% (19.3 mm) of the SWAT simulated mean annual rainfall (1176.9 mm) is converted into groundwater recharge in the watershed. The potential recharge zones categorized as very poor, poor, moderate and high zones have area coverages of 0.58% (20.8 km 2 ), 22.4% (798 km 2 ), 60.9% (2169 km 2 ), and 16.2% (576 km 2 ), respectively. The potential recharge zones after validation over boreholes and wells data indicated that the Afram Plains area is dominated by the moderate potential zone.

摘要 : The variational calculus of time-scale non-shifted systems includes both the traditional continuous and traditional significant discrete variational calculus. Not only can the combination of Δ and ∇ derivatives be beneficial to obtaining higher convergence order in numerical analysis, but also it prompts the time-scale numerical computational scheme to have good properties, for instance, structure-preserving. In this letter, a structure-preserving algorithm for time-scale non-shifted Hamiltonian systems is proposed. By using the time-scale discrete variational method and calculus theory, and taking a discrete time scale in the variational principle of non-shifted Hamiltonian systems, the corresponding discrete Hamiltonian principle can be obtained. Furthermore, the time-scale discrete Hamilton difference equations, Noether theorem, and the symplectic scheme of discrete Hamiltonian systems are obtained. Finally, taking the Kepler problem and damped oscillator for time-scale non-shifted Hamiltonian systems as examples, they show that the time-scale discrete variational method is a structure-preserving algorithm. The new algorithm not only provides a numerical method for solving time-scale non-shifted dynamic equations but can be calculated with variable step sizes to improve the computational speed.

摘要 : The urban residential regeneration strongly supported by the 14th five-year plan of China should achieve social sustainability. Assessing residents' satisfaction with the housing quality and living environment is essential for social sustainability and, therefore, should be considered in any transformation process. This study investigates which factors affect residents' satisfaction significantly in high-dense resettlement neighbourhoods, focusing on housing conditions and the community environment. The selected case study is Nanhuan Village, a large resettlement neighbourhood in Suzhou built in the early "80s with medium-density multi-storey buildings and partly transformed with high-density high-rises in 2010. The study analyses residents" satisfaction before and after the regeneration and adopts a mixed research method: in-depth interviews with community managers and designers, fieldwork, and a structured questionnaire survey with residents to determine the influencing factors of satisfaction analysed by a structural equation model. The study identifies 24 indicators and the results highlight what matters for the residents: "community environment", "property management", and "surrounding facilities" are the factors that most significantly impact the residents' satisfaction, even though there are different opinions between the residents of the old part and the regenerated part. The results are surprising: it is not the residential unit that mostly impacts the assessment—once a decent dwelling is provided—but the urban environment. The results also reveal that the densification realized by the transformation is not perceived as a problem. The results of this study can contribute to the definition of the government's urban regeneration policy.

摘要 : In this paper, we consider a rearrangement minimization problem related to a quasilinear equation with two independent data functions. First, we demonstrate that the equation has a unique ground state solution for each pair of the given data functions. Next, we prove that the corresponding rearrangement minimization problem is solvable. Finally, we prove the uniqueness and symmetry of the solution of the minimization problem if the domain is a ball centered at the origin. © 2022 Journal of Nonlinear Functional Analysis.

摘要 : Herein a rich, Se-nanoparticle modified Mo-W18O49 nanocomposite as efficient hydrogen evolution reaction catalyst is reported via hydrothermal synthesized process. In this work, Na2SeSO3 solution and selenium powder are used as Se precursor material. The structure and composition of the nanocomposites are characterized by X-ray diffraction (XRD), high-resolution field emission scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), EDX spectrum analysis and the corresponding element mapping. The improved electrochemical properties are studied by current density, and EIS analysis. The as-prepared Se modified Mo-W18O49 synthesized via Na2SeSO3 is investigated by FE-SEM analysis and found to exhibit spherical particles combined with nanosheets. This special morphology effectively improves the charge separation and transfer efficiency, resulting in enhanced photoelectric behavior compared with that of pure Mo-W18O49. The nanomaterial obtained via Na2SeSO3 solution demonstrates a high HER activity and low overpotential of -0.34 V, allowing it to deliver a current density of 10 mA cm-2.

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 : Motion blur is one of the key factors that affect the image quality obtained by liquid crystal display (LCD) systems. The slow response of display systems, the hold type display characteristic, the smooth eye tracking, and the visual integral effect lead to the perceptual blur of dynamic images. In order to study the method for improving the dynamic image quality of LCD, the image motion compensation preprocessing model and LCD dynamic image perception effect simulation model are established based on the theory of smooth eye tracking. At the same time, different adaptive motion compensation preprocessing methods are proposed for binary eight-bit display systems and binary ten-bit display systems. Through visual perception experiments, the research carries out subjective evaluation and statistical analysis on the effect of dynamic image motion compensation. The results show that the compensation method for eight-bit display systems can significantly improve the perception effect of dynamic images, and the improvement rate is 11.11%; while the compensation method for ten-bit display systems can achieve the perception effect close to the original still images, and the improvement rate is 112.75%. The research results can provide a theoretical reference for improving the dynamic image quality of LCD systems.

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.