Numerical solution of bed load transport equations using discrete least squares meshless (DLSM) method

The discrete least squares meshless (DLSM) method is extended in this paper for solving coupled bedload sediment transport equations. The mathematical formulation of this model consists of shallow water equations for the hydrodynamical component and an Exner equation expressing sediment continuity for the bedload transport. This method uses the moving least squares (MLS) function approximation to construct the shape functions and the minimizing least squares functional method to discretize the system of equations. The method can be viewed as a truly meshless method as it does not need any mesh for both field variable approximation and the construction of system matrices; it also provides the symmetric coefficient matrix. In the present work, several benchmark problems are studied and compared with the work of other researchers; the proposed method shows good accuracy, high convergence rate, and high efficiency, even for irregularly distributed nodes. At the end, a real test problem is performed to show and verify the main benefit and applicability of the proposed method to cope with complex geometry in practical problems.     

Optimal Sensor Placement Method Considering the Importance of Structural Performance Degradation for the Allowable Loadings for Damage Identification

Considering the importance of damage for the structural performance and for decreasing the identification error, this paper proposes an optimal sensor placement method based on a weighted standard deviation norm (WSDN) index. The standard deviation of the identified damage parameters is solved using the series expansion theory and probabilistic method to quantify the effect of a measurement error on damage identification. The damage estimation weight (DEW) index, which can reflect the importance of each element in the structural capabilities, is established based on a performance-damage curve. A significant DEW for a specified element indicates that the element is important for the structure and that its identification error should be small. The WSDN index is obtained from the Hadamard product of the standard deviations (SDs) and DEWs. Thus, the identification error of the entire structure is measured using the weighting coefficient. The optimal sensor placement (OSP) procedure is performed by minimizing the WSDN index. The proposed method can clearly decrease the uncertainties of the identification results for the important elements. Other OSP criteria, including the condition number, information entropy, and standard deviation norm, which aim to decrease the identification error, are discussed in this paper for comparison with the proposed method. Two numerical examples and an experiment, which pertain to the deformation performance, buckling features, and dynamic characteristics, are discussed to verify the advantages of the proposed method.     

Stochastic chemo-physical-mechanical degradation analysis on hydrated cement under acidic environments

The accumulation of material degradation under contact with aggressive aqueous environments could lead to reduced structural reliability. In terms of hydrated cementitious materials, such interactions often result in the chemo-physical-mechanical (CPM) degradation, which represents a multiphysics process of high non-linearity and complexity. By further considering the inevitable uncertainties associated with both the materials and the serving conditions, solving such a process requires novel probabilistic approaches. This paper presents a stochastic chemo-physical-mechanical (SCPM) degradation analysis on the hydrated cement under acidic environment. The SCPM analysis consists of modelling the stochastic chemophysical degradation by finite element method, and assessing the mechanical deterioration through analytical micromechanics. The proposed modelling framework couples the conventional Monte Carlo Simulation with a novel support vector regression algorithm. The present method is able to not only address the detailed degradation mechanisms, but also ensure low computational costs for an accurate SCPM degradation assessment.     

Evolution of single nanobubbles through multi-state dynamics

Nanobubble is a rising research field, which attracts more and more attentions due to its potential applications in medical science, catalysis, electrochemistry and etc. To better implement these applications, it is urgent to understand one of the most important mechanisms of nanobubbles, the evolution. However, few attentions have been paid in this aspect because of the methodology difficulties. Here we successfully used dark-field microscopy to study the evolution process of single nanobubbles generated from formic acid dehydrogenation on single Pd-Ag nanoplates. We found some of the nanobubbles in this system can exhibit three distinct states representing different sizes, which can transform among each other. These transitions are not direct but through some intermediate states. Further kinetic analysis reveals complicated mechanisms behind the evolution of single nanobubbles. The results acquired from this study can be applicable to nanobubble systems in general and provide insights into the understanding of mechanisms affecting the stability of nanobubbles and their applications.     

Research on adhesion strength and optical properties of SiC films obtained via RF magnetron sputtering

SiC is widely used in various mechanical applications as a protective film because of its strength, thermal stability and good mechanical hardness. Here, amorphous SiC thin films with AlN as a buffer layer were deposited on glass and Si substrates through RF magnetron sputtering at different RF powers. The influence of the AlN buffer layer thickness on the morphological and the mechanical properties of the composite films was investigated. Results demonstrate that the AlN buffer layer can effectively improve the adhesion strength of SiC thin films, which has increased gradually from 26.78 N to 37.66 N. The transmittance of SiC thin films was measured using a UV–Vis–NIR spectrophotometer over a spectral range of 300–1200 nm. The average transmittance of SiC films decreases with increasing RF power, and their optical band gap values have varied from 3.31 eV to 3.50 eV.     

Theoretical study of the effect of the Coulomb blockade and Kondo resonance in the density of states using self-consistent field approximation

In a recent paper, we theoretically investigated the density of states of the composite channel–contact system in the Coulomb and Kondo regimes using the self-consistent field approximation. There are the main experimental observations of vibration features in the Coulomb blockade [H. Park et al., Nature (London) 407, 57 (2000)] and Kondo [L. H. Yu et al., Phys. Rev. Lett. 93, 266802 (2004)] regimes. In the Kondo regime, our results show that one peak at $E=\mu$ can be observed in the density of states at low temperatures (0.0026 eV ≤ k_BT ≤ 0.0000026 eV). Also, the real part of ∑₃ has one minimum peak at $E=-\mu$ and the real par of ∑₂ has one maximum peak at $E=-\mu$ for 0.01 ≤ μ ≤ 0.07 in the Kondo regime at low temperatures.     

Cooperative coupling of photocatalytic production of H2O2 and oxidation of organic pollutants over gadolinium ion doped WO3 nanocomposite

This work reported the lanthanide ion (Gd³⁺) doped tungsten trioxide (Gd-WO₃) nanocrystal for remarkable promoted photocatalytic degradation of organic pollutants and simultaneous in-situ H₂O₂ production. With doped lanthanide ion (Gd³⁺), Gd-WO₃ showed a much broad and enhanced solar light absorption, which not only promoted the photocatalytic degradation efficiency of organic compounds, but also provided a suitable bandgap for direct reduction of oxygen to H₂O₂. Additionally, the isolated Gd³⁺ on WO₃ surface can efficiently weaken the *OOH binding energy, increasing the activity and selectivity of direct reduction of oxygen to H₂O₂, with a rate of 0.58 mmol L⁻¹ g⁻¹ h⁻¹. The in-situ generated H₂O₂ can be subsequently converted to ^•OH based on Fenton reaction, further contributed to the overall removal of organic pollutants. Our results demonstrate a cascade photocatalytic oxidation-Fenton reaction which can efficiently utilize photo-generated electrons and holes for organic pollutants treatment.     

Epitaxial growth of borophene on substrates

Borophene, a two-dimensional (2D) planar boron sheet, has attracted dramatic attention for its unique physical properties that are theoretically predicted to be different from those of bulk boron, such as polymorphism, superconductivity, Dirac fermions, mechanical flexibility and anisotropic metallicity. Nevertheless, it has long been difficult to obtain borophene experimentally due to its susceptibility to oxidation and the strong covalent bonds in bulk forms. With the development of growth technology in ultra-high vacuum (UHV), borophene has been successfully synthesized by molecular beam epitaxy (MBE) supported by substrates in recent years. Due to the intrinsic polymorphism of borophene, the choice of substrates in the synthesis of borophene is pivotal to the atomic structure of borophene. The different interactions and commensuration of borophene on various substrates can induce various allotropes of borophene with distinct atomic structures, which suggests a potential approach to explore and manipulate the structure of borophene and benefits the realization of novel physical and chemical properties in borophene due to the structure–property correspondence. In this review, we summarize the recent research progress in the synthesis of monolayer (ML) borophene on various substrates, including Ag(1 1 1), Ag(1 1 0), Ag(1 0 0), Cu(1 1 1), Cu(1 0 0), Au(1 1 1), Al(1 1 1) and Ir(1 1 1), in which the polymorphism of borophene is present. Moreover, we introduce the realization of bilayer (BL) borophene on Ag(1 1 1), Cu(1 1 1) and Ru(0 0 0 1) surfaces, which possess richer electronic properties, including better thermal stability and oxidation resistance. Then, the stabilization mechanism of polymorphic borophene on their substrates is discussed. In addition, experimental investigations on the unique physical properties of borophene are also introduced, including metallicity, topology, superconductivity, optical and mechanical properties. Finally, we present an outlook on the challenges and prospects for the synthesis and potential applications of borophene.