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The safety and reliability of high-speed train electric traction systems are crucial. However, the operating environment for China Railway High-speed (CRH) trains is challenging, with severe working conditions. Dataset imbalance further complicates fault diagnosis. Therefore, conducting fault diagnosis for high-speed train electric traction systems under data imbalance is not only theoretically important but also crucial for ensuring vehicle safety. Firstly, when addressing the data imbalance issue, the fault diagnosis mechanism based on support vector machines tends to prioritize the majority class when constructing the classification hyperplane. This frequently leads to a reduction in the recognition rate of minority-class samples. To tackle this problem, a self-tuning support vector machine is proposed in this paper by setting distinct penalty factors for each class based on sample information. This approach aims to ensure equal misclassification costs for both classes and achieve the objective of suppressing the deviation of the classification hyperplane. Finally, simulation experiments are conducted on the Traction Drive Control System-Fault Injection Benchmark (TDCS-FIB) platform using three different imbalance ratios to address the data imbalance issue. The experimental results demonstrate consistent misclassification costs for both the minority- and majority-class samples. Additionally, the proposed self-tuning support vector machine effectively mitigates hyperplane deviation, further confirming the effectiveness of this fault diagnosis mechanism for high-speed train electric traction systems. [ABSTRACT FROM AUTHOR]

There is an increasing interest in the affine formation control of multi-agent systems, because it can change the centroid, orientation and scale of the formation by controlling only a few leaders. In this paper, the fault-tolerant affine formation control problem is addressed for double-integrator multi-agent systems with partial loss of efficiency and bias faults. Firstly, in order to track the leaders with dynamically changing accelerations, an acceleration observer with prescribed time convergence is proposed, which can estimate the ideal acceleration for each follower. Then, based on the acceleration observer, a fault-tolerant control algorithm is given. A new Lyapunov function candidate is constructed, based on which a sufficient condition to achieve the control objective is derived. Theoretical analysis shows that the formation tracking error can converge to zero within a prescribed time, and remain in a small neighborhood of zero after that time. Finally, numerical simulations are given to show the effectiveness of the proposed algorithm and compare it with existing results. [ABSTRACT FROM AUTHOR]

The vertical stacking of various two-dimensional (2D) layered materials to create van der Waals heterostructures (vdWHs) has received great attention as a promising material for developing nanoelectronic and optoelectronic devices. This is because such structures can inherit the unique and favorable properties of a single 2D material. In this study, a SnSe2/MoSe2 vdWH model was built for the first time using the first-principles approach, and its electronic and optical properties were systematically investigated. The results reveal that the SnSe2/MoSe2 vdWH exhibits a type-II heterostructure with a 0.167 eV indirect band gap, which facilitates the separation of photogenerated electron–hole pairs. Notably, the electrical characteristics of the SnSe2/MoSe2 vdWH can be easily controlled by applying an external electric field or biaxial strain. Specifically, a positive electric field or tensile strain narrows the band gap, whereas a negative electric field or compressive strain widens the band gap. The energy band alignment shifts from a type-II to a type-I configuration when a negative electric field of E = −0.6 V Å–1 or a compressive strain of 10% is applied. Furthermore, SnSe2/MoSe2 vdWHs exhibit improved optical absorption across the visible to ultraviolet regions compared to the individual monolayers of SnSe2 and MoSe2. Additionally, the absorption can be influenced by external tension and electric fields. Specifically, under significant compressive strains (10%), the ultraviolet absorption peak reaches 33.5%. Interestingly, a red shift occurs with tensile strain or a negative electric field, whereas a blue shift occurs with compressive strain or a positive electric field. The proposed SnSe2/MoSe2 vdWH in this study offers valuable insights into electronic and optoelectronic device development, particularly in the context of photovoltaic devices, where enhanced ultraviolet absorption can lead to improved light-to-electricity conversion efficiency. [ABSTRACT FROM AUTHOR]

TiO2 is a dielectric material with excellent photocatalytic and photochemical properties. The conversion of TiO2 from an amorphous to crystalline phase significantly improves the photocatalytic activity of TiO2. However, the crystallization behavior of TiO2 during annealing has been little studied in the field of molecular dynamics. In this paper, the crystallization behavior of TiO2 during annealing under different conditions was analyzed using molecular dynamics simulation. To investigate the phase transition process of TiO2, the melting point temperature of the system was calculated by mean square displacement at about 2400 K. The effect of size on structural stability was explored. The radial distribution function and x-ray diffraction curves revealed that the anatase phase appeared over 800 K. Moreover, with the increase in annealing temperature, the anatase content in TiO2 first increased and then decreased, and the rutile phase gradually increased. At a specific temperature, a structure is formed where rutile and anatase coexist. Anatase atoms compete with rutile atoms, and by increasing the temperature, anatase is converted to rutile. The amorphous structure is reduced at high temperatures, improving the crystalline quality. The crystallization behavior of the amorphous structure can improve the photocatalytic efficiency of TiO2. TiO2 nanometers have good prospect for application. Therefore, studying the crystallization behavior of TiO2 is essential. [ABSTRACT FROM AUTHOR]

In this study, a large-scale kerosene-fueled oblique detonation engine with a design point of Mach 10 is proposed. The flow combustion characteristics and the propulsive performance considering the wall viscous drag of the detonation engine are investigated using numerical simulation methods with a detailed combustion mechanism. The accuracy of the numerical results is verified by comparing it with the detonation wave pole curve of kerosene fuel. The result demonstrates that the combined injection method consisting of wall and center-strut injectors can meet the requirements of fuel mixing in the oblique detonation engine and a stabilized oblique detonation wave is successfully formed in the combustor. The decrease in the fuel equivalent ratio leads to an increase in the non-uniformity of the temperature distribution behind the detonation wave and the decrease in the wave angle. The advantage of the oblique detonation wave in hypersonic propulsion is its easy adjustment and can achieve flight over a wide-speed range. The combustion heat release behind the wave is closer to the upper part of the wave surface as the incoming Mach number decreases. The oblique detonation engine proposed in this study can still generate stable net specific impulse at non-design point flow Mach numbers. The net specific impulse can reach 715 s at a non-design point speed of Mach 8. It proves the feasibility of wide-speed range flight applications of oblique detonation engines. [ABSTRACT FROM AUTHOR]

Metasurfaces play a crucial role in trapping electromagnetic waves with specific wavelengths, serving as a significant platform for enhancing light-matter interactions. In all kinds of dynamic modulation metasurfaces, electro-optic modulation metasurfaces have attracted much attention due to its advantages of fast, stable and high efficiency. In order to respond to the extremely weak refractive index change of the electro-optical effect of the materials, the metasurfaces are required to support optical signals with high Q values. The quasi-bound state in the continuum (Q-BIC) is often used to enhance the light-field modulation capability of metasurfaces and to improve the modulation sensitivity of electro-optic modulators due to its ability to generate high Q-factor resonances. However, the design of an electro-optic modulation metasurface that facilitates the application of voltage and achieves modulation efficiency of nearly 100% is still in urgent need of development. In this study, single-crystal BTO metasurfaces are modeled using finite-difference time-domain method, and the structural symmetry is broken to introduce a Q-BIC resonance to generate a high Q-factor optical signal of 2.45 × 10 4 for high-depth electro-optic modulation. By simulating an applied electric field of 143 V/mm on the metasurface, a slight refractive index change of BTO of 8 × 10 -4 was produced, leading to an electro-optical intensity modulation depth of 100%. Furthermore, the nanostructure of the metasurface was carefully designed to facilitate nano-fabrication and voltage application, and it is ideal for the development of low-power, CMOS-compatible, and miniaturized electro-optic modulation devices. Although the results of this study are based on simulations, they provide a crucial theoretical basis and guidance for the realization of efficient and realistic design of dynamic metasurfaces.