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C4F7N/CO2 gas mixtures have attracted extensive attention because of their excellent insulating properties and environmental friendliness. High electrical and thermal stability is an important indicator for evaluating their performance, but there have been few molecular dynamics studies of their decomposition mechanisms. In this study, using ReaxFF molecular dynamics simulations and quantum chemistry theory, the decomposition mechanism of a C4F7N/CO2 gas mixture and the effect of the O2 content on the decomposition of the mixture were simulated on the microscopic level. It was found that there are three main decomposition pathways of C4F7N molecules, of which the generation of C3F4N⋅ and CF3⋅ free radicals is the most likely to occur. COF2 is the main oxygen-containing product of the C4F7N/CO2 gas mixture, and its generation is significantly affected by the simulation time and temperature. COF2 can be regarded as the characteristic decomposition product of the C4F7N/CO2 gas mixture. The addition of O2 slightly promotes the decomposition of C4F7N, whereas the maximum decomposition rate of CO2 decreases by 0.3% and 1% after the addition of 2% and 8% O2, respectively. Relevant results of this research can provide a theoretical basis and guidance for research into the performance of C4F7N/CO2 gas mixtures and practical engineering applications of these mixtures in the future. [ABSTRACT FROM AUTHOR]

SF6 is widely used in gas switchgear but has a strong greenhouse effect. The development of an environment-friendly switchgear that can replace SF6 is a current research hotspot. As a SF6 alternative technology, vacuum arc-extinguishing chamber plus clean air insulation has shown high application prospects. The clean air inside the switchgear decomposes under the effect of high temperature and discharge; however, only a few studies focused on its decomposition mechanism. In this work, the decomposition mechanism of clean air and the effect of temperature on the decomposition are simulated at the atomic level based on ReaxFF (Reactive force field) molecular dynamics and quantum chemistry theory. Results showed that the decomposition of clean air mainly generates NO, NO2, and N2O. NO is the main product at high temperatures and thus can be the characteristic decomposition product of clean air. The clean air has good self-recovery characteristics, and its decomposition can be substantially promoted by increasing the temperature. The decomposition rates of N2 and O2 under 3000 K can reach 7.00% and 8.00%, respectively, which are twice and four times those under 2000 K. These results can provide theoretical basis and engineering guidance for the development of environment-friendly switchgear with vacuum arc-extinguishing chamber plus clean air insulation. [ABSTRACT FROM AUTHOR]

Traditional metamaterial systems usually own a low Q factor due to the strong absorption and radiation loss. Fano resonances in ultrathin metasurfaces provide an efficient method for solving the issue. In this work, we theoretically and experimentally study the trapped-mode resonance in rectangular-hole dimers with broken symmetry. Compared to the asymmetric particle dimers that have been widely investigated, the asymmetric hole dimers in freestanding metal screens present an all-metallic platform for engineering the high-Q resonances. With the experiments, a significantly increased Q factor of ∼200 has been achieved in the microwave region. Numerical simulations show that, in comparison with the incident field, the hole electric field (and intensity) can be increased by ∼127 times (and ∼16 000 times). Moreover, the evolution characteristic of the trapped-mode resonance with the structural parameters has been studied systematically. The inversely quadratic relationship between the Q factor and asymmetric parameter, proposed primarily for the particle dimers [Koshelev et al., Phys. Rev. Lett. 121, 193903 (2018)], is found to work well for the asymmetric hole dimers. [ABSTRACT FROM AUTHOR]

The microscopic properties of nonequilibrium arc plasma have great significance for researching the breaking capacity of SF6 circuit breakers and constructing arc plasma simulation models. The polytetrafluoroethylene (PTFE) vapor generated by the ablation of the nozzle material significantly affects the SF6 arc plasma particles and thus affects the microscopic properties of the nonequilibrium arc plasma. At present, the calculation of the microscopic properties of nonequilibrium SF6–PTFE arc plasma has not been reported, mainly because the basic data for the chemical reaction mechanism and chemical reaction rate in the plasma cannot be obtained effectively. In this paper, quantum chemistry was used to theoretically research the reaction mechanisms and rates between CF3, CF2, and CF radicals and SF6, SF5, SF4, SF3, SF3, SF2, and SF in SF6–PTFE arc plasma at 298–10 000 K. A total of 18 chemical reactions are included. Structural optimizations, vibrational frequency calculations, and zero-point energy calculations for the reactants, products, and transition states were performed at the B3LYP/6-311++G(d,p) level of theory. The single-point energies of all species were obtained at the CCSD(T)/aug-cc-PVTZ level. The reaction rates of all reactions between 298 and 10 000 K were obtained by using transition state theory. The reaction rates were successfully fitted using the Arrhenius equation and the three-parameter Arrhenius equation. It has found that reactions between CF2 and fluoro sulfides have higher potential energies. Reactions R13, R7, R14, and R8 exhibit higher reaction rates at 298–10 000 K, whereas R3, R4, R5, and R6 have lower reaction rates. This work can provide theoretical guidance for research on nonequilibrium SF6–PTFE and SF6–CF4 arc plasma microscopic properties. [ABSTRACT FROM AUTHOR]

We describe a high intensity metastable Kr source based on a helical resonator RF discharge. By adding an external B-field to the discharge source, the metastable Kr flux is enhanced. The effect of geometric configuration and magnetic field strength has been studied and optimized experimentally. Compared to the helical resonator discharge source without an external B-field, the new source showed an enhancement factor of 4–5 in producing metastable Kr beams. This improvement has a direct impact on the radio-krypton dating applications as it can increase the atom count rate, resulting in a higher analytical precision. [ABSTRACT FROM AUTHOR]

Several deep learning partial discharge (PD) diagnostic approaches have been developed in recent years to guarantee the security and stability of gas-insulated switchgear (GIS). The centralized training method requires multiple clients to jointly obtain as much data as possible to train the model to achieve excellent performance, which is impractical due to conflicts of interest and privacy protection. Furthermore, because of differences in the distribution of client data and the presence of a small sample, achieving high-precision and robust diagnosis for each client is an urgent problem. To that end, a novel personalized federated meta-learning (FML) is proposed in this paper to address the aforementioned issues. It develops reliable and personalized PD diagnosis models by collaborating with multiple clients and solves the problem of small sample diagnosis through scenario training under the premise of protecting data privacy. The experimental results show that the FML proposed can diagnose GIS PD with high precision and robustness for each client while maintaining privacy. The diagnostic accuracy of the FML proposed in this paper, especially for on-site unbalanced small sample clients, is 93.07%, which is significantly higher than that for other methods. It serves as a model for the collaborative development of an effective GIS PD diagnostic model. [ABSTRACT FROM AUTHOR]

Blue phase liquid crystals (BPLCs) are emerging as a promising candidate for tunable three-dimensional (3D) photonic crystals. Uniform monodomain BPLCs with a large temperature range are needed to achieve higher performance for photonic applications. Here, we experimentally demonstrated monodomain polymer stabilized blue phase liquid crystals (PS-BPLCs) induced by a long-lasting electric field. The PS-BPLCs with a single crystal orientation can be obtained with appropriate electrical treatment, and they also possess a large temperature range of 70 °C including room temperature. The physical mechanism behind their spectral properties, phase transition temperature, and the morphology of crystal growth process under different electric fields are investigated with detailed experimental analysis. This work helps further understanding of crystal nucleation and growth of PS-BPLCs in electric field and also can expedite the development of PS-BPLC based tunable 3D photonic crystal devices. [ABSTRACT FROM AUTHOR]

Geometrical structures and operating performance of volutes used in centrifugal pumps are assessed in cross sections. By a volute, we mean the wetted part surrounding the impeller in a pump that converts the kinetic energy of water into potential energy. It is important to develop improved design principles and approaches for volutes to reduce hydraulic loss and increase the efficiency of pumps. However, when designing volutes, pump designers often neglect a key factor related to pump efficiency, namely, the energy loss due to the friction at the volute sidewall is directly proportional to the wetted perimeter of the cross section. In this paper, we show that the length of the wetted perimeter of the cross section is mathematically proportional to the friction loss in the volute. In addition, we present the design principles and calculation process to minimize the wetted perimeters of two kinds of cross section based on the velocity coefficient method using the same statistical data. The structures and shapes of the new cross sections are completely different from those of traditional volutes. Moreover, two different volutes with different cross sections are numerically investigated using a verified computational fluid dynamics technique. Both the head and the efficiency of the pump with the new volute are higher than those of a conventional pump under all working conditions. This paper provides a new design approach for the energy-saving volutes of centrifugal pumps. [ABSTRACT FROM AUTHOR]

An abnormal sub-threshold leakage current is observed at high temperature in amorphous indium-gallium-zinc-oxide thin film transistors (a-IGZO TFTs). This phenomenon occurs due to a reduced number of defects in the device's a-IGZO active layer after the device has undergone N2O plasma treatment. Experimental verification shows that the N2O plasma treatment enhances the thin film bonding strength, thereby suppressing the formation of temperature-dependent holes, which are generated above 400 K by oxygen atoms leaving their original sites. The N2O plasma treatment devices have better stability performance than as-fabricated devices. The results suggest that the density of defects for a-IGZO TFTs with N2O plasma treatment is much lower than that in as-fabricated devices. The N2O plasma treatment repairs the defects and suppresses temperature-dependent sub-threshold leakage current. [ABSTRACT FROM AUTHOR]

Existing techniques for stabilizing and functionalizing metal nanostructures required precise control of complex procedures and probably introduce undesirable impurities. We herein report an arc-discharge chemical vapor deposition strategy for the synthesis of chemically heterogeneous core/shell metal/oxide nanocapsules Fe/TiFe2O4, Fe/MnFe2O4, and Fe/Al2O3. A universal formation mechanism based on the co-effect of oxygen potential and surface energy is further proposed, derived from fundamental thermodynamics. Such core/shell nanocapsules, integrated with tunable components, present an effective manipulability of microwave absorption at expected frequency, originating from the various dielectric behaviors of the heterogeneous oxide shells. [ABSTRACT FROM AUTHOR]

Both the chemical reaction mechanism and rate can largely explain the formation mechanism of the by-products of SF6. By understanding this mechanism, we can develop and improve models of the chemical kinetics of SF6 decomposition under discharge. Using quantum chemistry, this study compares the reaction mechanisms and rates of SF6−, SF5−, SF4−, and SF3− and H2O under discharge at 298 K–12 000 K and reveals the formation mechanism of their anionic by-products, i.e., SOF4−, SOF3−, SOF2−, and SOF−. The key parameters such as the reaction equation and reaction rate to improve the chemical kinetic models under partial and arc discharges were then obtained. In this study, the structural optimizations, vibrational frequencies, and zero-point energies of the reactants, products, complexes, intermediates, and transition states were calculated at the B3LYP/6-311G(d,p) level. The single-point energies of all species were calculated at the CCSD(T)/aug-cc-PVTZ level. The strengths and sites of weak interactions were determined from the electrostatic potential of the molecular surface, and the reaction rates were obtained using transition state theory. It has been found that SF6−, SF5−, SF4−, and SF3− combined with H2O to form weak-interaction complexes dominated by hydrogen bonding, thus providing the initial conditions for R1, R2, R3, and R4, respectively. All four reactions were composed of multiple elementary reactions with the first step being the rate-determining step. Moreover, compared to their corresponding reactions of SF5, SF4, SF3, and SF2 with H2O, they achieved lower potential energy barriers and higher reaction rates. Note that the reaction rates decreased in the following order: R3 > R2 > R1 > R4. [ABSTRACT FROM AUTHOR]

This letter describes an adjusted antisymmetric angle ply laminate that is able to twist as a result of temperature-dependent deformation. A theoretical explanation for this twisting ability is presented and the adjusted architecture of the proposed laminate is described. The effects of fiber and matrix volume fractions, laminate angle, total laminate thickness, and temperature range on the torsion of the laminate are analyzed. A sample of the proposed microlaminate is produced by a microfabrication process and tested as the temperature is increased from room temperature to 80 °C. Microscopy images reveal that the microlaminate twists by more than 180° within a length of 200 μm. The proposed material and its twisting ability show great potential for application in microrobotic actuators. [ABSTRACT FROM AUTHOR]

In pulsed power systems, pulsed currents with risetimes from nanosecond to microsecond can be effectively measured by self-integrating Rogowski coils. Appropriate design of the structure and the integrating resistor is crucial to the high-frequency response of a coil. In this paper, several novel designs of Rogowski coil's integrating resistors were proposed and tested. Experimental results showed that the optimized coil could response square waves with fronts of ~1.5 ns and had a sensitivity of ~0.75 V/kA. The maximal peak current was designed as 100 kA. [ABSTRACT FROM AUTHOR]

BaxSr1-xTiO3 ceramics with x ranging from 0 to 1 were prepared by direct current arc discharge technique and studied by means of x-ray diffraction (XRD) and Raman spectroscopy. The cubic- tetragonal ferroelectric phase transition in BaxSr1-xTiO3 ceramics was found to occur at x ≈ 0.75. XRD investigation of as-grown BaTiO3 ceramics revealed co-existence of tetragonal and hexagonal modifications with a small amount of impurity phase BaTi4O9. No evidences of hexagonal phase were observed in Raman spectra of as-grown BaTiO3 ceramics, while Raman peaks related to hexagonal phase were clearly observed in the spectrum of fine-grain powders prepared from the same ceramics. A core-shell model for BaTiO3 ceramics prepared by direct current arc discharge technique is proposed. Absence of the hexagonal phase in any BaxSr1-xTiO3 solid solution with x<1 is discussed in the frame of specific atomic arrangement. [ABSTRACT FROM AUTHOR]

This letter investigates the degradation behavior under hot-carrier stress in InGaZnO thin film transistors with I- and U-shaped asymmetric electrodes. After hot-carrier stress, a serious Vt shift, as well as on-current and subthreshold swing degradations are observed in Id-Vg transfer curve under reverse mode. Moreover, it is found that the Vt instability is caused by hot-electron injection near the drain side, and this phenomenon which is verified by C-V measurement. Furthermore, the location of trapped hot-electron is estimated from the two-stage rise in the gate-to-drain/gate-to-source capacitance curves and then verified by the simulation tool. [ABSTRACT FROM AUTHOR]

A polarization independent switchable phase grating based on polymer stabilized blue phase liquid crystal is proposed. A high efficiency of the phase grating has been achieved because of the sharp rectangular phase profile which shows good agreement with the simulation results. The diffraction efficiency of the 1st order is 38%, the response time is in the submillisecond range, and the phase grating is independent of the polarization of the incident light. The voltage-induced hysteresis characteristics are also investigated. [ABSTRACT FROM AUTHOR]

Investigates the critical thickness of an epilayer grown on a compliant substrate with the semiconductor-on-insulator configuration on the assumption that sliding boundary conditions hold along the interface between the thin crystal substrate and the amorphous underneath layer. Use of superposition and Fourier transformation.

This letter investigates the effect of temperature on hot-carrier stress-induced degradation behavior in InGaZnO thin film transistors. After hot-carrier stress at 25 °C, serious on-current and subthreshold swing degradations are observed due to trap state generation near the drain side. For identical stress performed at elevated temperatures, current degradation in the I-V transfer curve under reverse mode is gradually suppressed and the anomalous hump in the gate-to-drain capacitance-voltage curve becomes more severe. These suppressed degradations and the more severe hump can be both attributed to hole-trapping near the drain side due to high drain bias at high temperature. [ABSTRACT FROM AUTHOR]

In-cell touch sensor that can be integrated with display pixel circuit using dual gate InGaZnO thin-film transistor is proposed. Under bottom gate operation, device characteristics are not sensitive to light illumination. On the contrary, light can lead to evident subthreshold leakage when operated with top gate. This behavior allows touch sensor to be realized by sensing the ambient light using top gate operation, without affecting normal bottom gate operated devices in display pixel. Further, the proposed operation method of touch sensor needs no additional fabrication and cost, and even black matrix is not required either. [ABSTRACT FROM AUTHOR]