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The precise estimate of remaining useful life (RUL) is vital for the prognostic analysis and predictive maintenance that can significantly reduce failure rate and maintenance costs. The degradation-related features extracted from the sensor streaming data with neural networks can dramatically improve the accuracy of the RUL prediction. The Temporal deep degradation network (TDDN) model is proposed to make the RUL prediction with the degradation-related features given by the one-dimensional convolutional neural network (1D CNN) feature extraction and attention mechanism. 1D CNN is used to extract the temporal features from the streaming sensor data. Temporal features have monotonic degradation trends from the fluctuating raw sensor streaming data. Attention mechanism can improve the RUL prediction performance by capturing the fault characteristics and the degradation development with the attention weights. The performance of the TDDN model is evaluated on the public C-MAPSS dataset and compared with the existing methods. The results show that the TDDN model can achieve the best RUL prediction accuracy in complex conditions compared to current machine learning models. The degradation-related features extracted from the high-dimension sensor streaming data demonstrate the clear degradation trajectories and degradation stages that enable TDDN to predict the turbofan-engine RUL accurately and efficiently.

Imidazoles are widely used as curing agents and accelerators for fabricating crosslinked epoxy materials applied in electrical and electronic fields. However, the intrinsic chemical structure of imidazole derivatives would greatly influence the polymerisation process, and further change the electrical properties, which was not emphasised. To achieve an in-depth understanding, commonly used imidazole only containing pyridine-type nitrogen and imidazole with both pyridine and pyrrole-type nitrogen were selected in this study. Electrical properties including dielectric properties, volume resistivity, breakdown strength, and especially energy storage performances were systematically investigated. We figured out that higher breakdown strength, glass transition temperature, and lower dielectric loss can be achieved with imidazole containing pyrrole-type nitrogen. Structure-induced curing mechanism diversity and the generated differences in polymer network were highlighted. With the capability to incorporate into the polymer network, the dielectric constant/loss of epoxy cured by imidazole containing pyrrole-type nitrogen is less sensitive with variation in concentration and a high breakdown strength of 577.9 MV/m was achieved. On the contrary, conspicuous decrease in the breakdown strength and increase in dielectric loss of the epoxy cured by imidazole only containing pyridine-type nitrogen were observed, especially at high concentration. Moreover, we also found that the epoxy can be fabricated into films with an attractive energy storage density/efficiency of 1.1 J/cm3/97%@200 MV/m, which is twice of the commercial dielectric polypropylene film under the same electric field. © 2021 The Authors. High Voltage published by John Wiley & Sons Ltd on behalf of The Institution of Engineering and Technology and China Electric Power Research Institute.

Imidazoles are widely used as curing agents and accelerators for fabricating crosslinked epoxy materials applied in electrical and electronic fields. However, the intrinsic chemical structure of imidazole derivatives would greatly influence the polymerisation process, and further change the electrical properties, which was not emphasised. To achieve an in-depth understanding, commonly used imidazole only containing pyridine-type nitrogen and imidazole with both pyridine and pyrrole-type nitrogen were selected in this study. Electrical properties including dielectric properties, volume resistivity, breakdown strength, and especially energy storage performances were systematically investigated. We figured out that higher breakdown strength, glass transition temperature, and lower dielectric loss can be achieved with imidazole containing pyrrole-type nitrogen. Structure-induced curing mechanism diversity and the generated differences in polymer network were highlighted. With the capability to incorporate into the polymer network, the dielectric constant/loss of epoxy cured by imidazole containing pyrrole-type nitrogen is less sensitive with variation in concentration and a high breakdown strength of 577.9 MV/m was achieved. On the contrary, conspicuous decrease in the breakdown strength and increase in dielectric loss of the epoxy cured by imidazole only containing pyridine-type nitrogen were observed, especially at high concentration. Moreover, we also found that the epoxy can be fabricated into films with an attractive energy storage density/efficiency of 1.1 J/cm3/97%@200 MV/m, which is twice of the commercial dielectric polypropylene film under the same electric field. © 2021 The Authors. High Voltage published by John Wiley & Sons Ltd on behalf of The Institution of Engineering and Technology and China Electric Power Research Institute.

Imidazoles are widely used as curing agents and accelerators for fabricating crosslinked epoxy materials applied in electrical and electronic fields. However, the intrinsic chemical structure of imidazole derivatives would greatly influence the polymerisation process, and further change the electrical properties, which was not emphasised. To achieve an in-depth understanding, commonly used imidazole only containing pyridine-type nitrogen and imidazole with both pyridine and pyrrole-type nitrogen were selected in this study. Electrical properties including dielectric properties, volume resistivity, breakdown strength, and especially energy storage performances were systematically investigated. We figured out that higher breakdown strength, glass transition temperature, and lower dielectric loss can be achieved with imidazole containing pyrrole-type nitrogen. Structure-induced curing mechanism diversity and the generated differences in polymer network were highlighted. With the capability to incorporate into the polymer network, the dielectric constant/loss of epoxy cured by imidazole containing pyrrole-type nitrogen is less sensitive with variation in concentration and a high breakdown strength of 577.9 MV/m was achieved. On the contrary, conspicuous decrease in the breakdown strength and increase in dielectric loss of the epoxy cured by imidazole only containing pyridine-type nitrogen were observed, especially at high concentration. Moreover, we also found that the epoxy can be fabricated into films with an attractive energy storage density/efficiency of 1.1 J/cm3/97%@200 MV/m, which is twice of the commercial dielectric polypropylene film under the same electric field. © 2021 The Authors. High Voltage published by John Wiley & Sons Ltd on behalf of The Institution of Engineering and Technology and China Electric Power Research Institute.

The outstanding thermal properties, mechanical properties and large optical bandgap of hexagonal boron nitride (h-BN) make it very attractive for various applications in ultrathin 2D microelectronics. However, the synthesis of large lateral size and uniform h-BN thin films with a high breakdown strength still remains a great challenge. Here, we comprehensively investigated the effect of growth conditions on the thickness of h-BN films via low pressure chemical vapor deposition (LPCVD). By optimizing the LPCVD growth parameters with electropolished Cu foils as the deposition substrates and developing customized `` enclosure'' quartz-boat reactors, we achieved thickness-tunable (1.50-10.30 nm) growth of h-BN thin films with a smooth surface (RMS roughness is 0.26 nm) and an ultra-large area (1.0 cm x 1.0 cm), meanwhile, the as-grown h-BN films exhibited an ultra-high breakdown strength of similar to 10.0 MV cm(-1), which is highly promising for the development of electrically reliable 2D microelectronic devices with an ultrathin feature.

Study on nanosecond pulse flashover characteristics of vacuum insulator surface is extremely significant for designing reliable pulse power devices. The rising steepness of pulse voltage greatly affects the flashover process. In this study, a two-dimensional model based on secondary electron emission avalanche (SEEA) scheme was established to study the relationship between pulse rising steepness and flashover performance. Particle-in-cell (PIC) method was used to describe multiplication and propagation behaviors of the charged particles during the flashover process. And collisional ionization process between primary electrons and desorbed gas was described by the Monte Carlo collision (MCC) method. The number evolution, distribution of charged particles, and field distribution at different moments during the flashover process are successfully presented in the simulation. Furthermore, the model shows that higher pulse voltage rising steepness will lead to higher flashover voltage, which accords well with our group's previous experimental results.

Study on nanosecond pulse flashover characteristics of vacuum insulator surface is extremely significant for designing reliable pulse power devices. The rising steepness of pulse voltage greatly affects the flashover process. In this study, a two-dimensional model based on secondary electron emission avalanche (SEEA) scheme was established to study the relationship between pulse rising steepness and flashover performance. Particle-in-cell (PIC) method was used to describe multiplication and propagation behaviors of the charged particles during the flashover process. And collisional ionization process between primary electrons and desorbed gas was described by the Monte Carlo collision (MCC) method. The number evolution, distribution of charged particles, and field distribution at different moments during the flashover process are successfully presented in the simulation. Furthermore, the model shows that higher pulse voltage rising steepness will lead to higher flashover voltage, which accords well with our group's previous experimental results.