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The solid-state transformer (SST) was regarded as the ideal power router in the energy Internet. However, the partial discharge (PD) in tightly packed SST is one of the main causes of interturn multilayer insulation premature failure. The effect of high-frequency (HF) electrical-thermal coupling stress on SST multilayer insulation's PD characteristics and failure mechanism is not clarified, which is investigated in this article. An HF PD measurement system is established, and a comparative study of the PD characteristics of multilayer polyimide (PI) insulation at different test frequencies and temperatures is explored. The experimental results show that when the frequency exceeds 10 kHz, the PD exhibits a rabbit-ear-like discharge pattern. However, the higher temperature will lead to lower PD inception voltage with large PD magnitudes, which may accelerate the degradation of interturn insulation. According to the phase-resolved PD, PD magnitude, PD number, and discharge phenomenon of the PI layer, the failure process of the multilayer PI system is divided into three stages: electric tree development, electric tree breakdown, and point prebreakdown. In addition, we propose the PD development model of multilayer PI insulation. The research results can provide a theoretical reference for elucidating the PD mechanism under HF stresses.

As a passive driving method for liquids, capillary flow has important value in the design of passive microfluidic chips and microreactors. To predict the behavior of fluid’s flow in vertical capillaries, this paper studies the different stages of passive filling of microfluidics in capillaries through numerical simulation and experimental verification, with a focus on the dynamic law of passive filling in vertical capillaries. The theoretical derivation is combined with numerical simulation, which not only obtains the conditions for the occurrence of the liquid’s surface oscillation in the capillaries but also gives the theoretical and predictive formulas for the flow law in vertical capillaries. This further clarifies whether a single factor in fluid’s properties and pipeline characteristics has an impact on capillary flow and quantified the magnitude of its impact. The simulation results are verified by experiments, and the reasons for the difference between the simulation results and the experimental data are explored; that is, when the fluid flows in the tube, the dynamic contact angle will affect the actual flow process. The statistical variation of the contact angle with fluid’s flow provides a certain reference value for the measurement and prediction of the dynamic contact angle in capillaries.

The identification of transition field factor boundary between streamer initiation dominated breakdown and streamer propagation dominated breakdown is important for understanding the breakdown mechanisms of transformer liquids and for the transformer insulation design in practice. Most previous studies focused on either very divergent field or nearly uniform field. This article reports on breakdown voltage tests with three transformer liquids in moderately uniform fields. The results show that the transition field factor boundary between streamer initiation dominated breakdown and streamer propagation dominated breakdown under negative lightning impulse is liquid-dependent. It is 9.6 for a mineral oil, 7.3 for a gas-to-liquid (GTL) oil, and 42.0 for a synthetic ester. The difference in the transition field factor boundary helps explain the observed breakdown voltage distinction among the three transformer liquids. In addition, the characteristics of negative streamers leading to breakdown were also investigated in the moderately uniform fields. Streamer mode transitions with gap distance were observed and clarified, which is from 1st mode streamer to 2nd mode streamer in both the mineral oil and GTL oil, while it is the 2nd mode streamer to fast streamer in the synthetic ester.

ABSTRACTDue to the uncertainty of user’s behaviour and other conditions, the design of energy efficiency improvement methods in buildings is challenging. In this paper, a building energy management method based on deep reinforcement learning is proposed, which solves the energy scheduling problem of buildings with renewable sources and energy storage system and minimises electricity costs while maintaining the user’s comfort. Different from model-based methods, the proposed DRL agent makes decisions only by observing the measurable information without considering the dynamic of the building environment. Simulations based on real data verify the effectiveness of the proposed method.

Fluids containing polymers are frequently utilized in the chemical industry and exhibit shear-thinning characteristics. The flow distribution of non-Newtonian fluids in parallelized microchannels is a key issue to be solved during numbering-up. Numbering-up means increasing the number of parallelized microchannels. In this study, a high-speed camera is used to explore the distribution of fluid flow as well as the uniformity and stability of droplets in conceptual asymmetrical parallelized microchannels. Cyclohexane and carboxymethylcellulose sodium (CMC) aqueous solutions are used as the continuous phase and dispersed phase, respectively. The effects of fluctuation of pressure difference around the T-junction, the hydrodynamic resistance in microchannels, and the shear-thinning property of fluids on flow distribution and droplet formation are revealed. The uniformity and stability of droplets in microdevices with various cavity settings are compared, and an optimal configuration is proposed. Finally, prediction models for the flow distribution of shear-thinning fluids in asymmetrical parallelized microchannels are established.

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Marmots are large ground squirrels, and 14 species have been reported in the world, including four species of marmots (Himalayan marmot, Tarbagan marmot, gray marmot and long-tailed marmot) living in China. Although these biological resources are abundant in China, information regarding their genetic features is lacking, hampering further study regarding them. The aims of this research were to evaluate genetic variations of four species of Chinese wild marmots, and analyzed kinship of these marmot populations. In the current study, we collected samples of four species of Chinese wild marmot and analyzed the effective allele number, gene diversity, the Shannon index, and polymorphism information to evaluate genetic variations using 13 microsatellite loci. Based on Nei’s genetic distance using the unweighted pair group method, we constructed a dendrogram to analyze the population kinship. We determined that all four Chinese marmot species had high genetic polymorphisms and departure from Hardy-Weinberg equilibrium. The Chinese marmots to be divided into two large groups: Himalayan marmot was independent group. Tarbagan marmot, gray marmot and long-tailed marmot were others; Tarbagan marmot and gray marmot showed a close kinship with each other, but long-tailed marmot did not have a close relationship with the other species. The high polymorphisms and the kinship of Chinese marmot populations were correlated with geographical terrain of their habitat. Himalayan marmot was characterized as living in unique alpine meadows in Qinghai-Tibet plateau and was affected by terrain; however, Tarbagan marmot, gray marmot and long-tailed marmot were characterized as living in grassland or alpine grassland and were not affected by terrain. Genetic features of Chinese wild marmots were investigated in this study. This may give using information regarding protection of Chinese wild marmot resource and further application of biomedical research.