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Purpose This paper aims to study the effects of MnO2 on the ZnO–Bi2O3-based varistor prepared via flash sintering (FS) Design/methodology/approach MnO2-doped ZnO–Bi2O3-based varistors were successfully prepared by the FS with a step-wise increase of the .current in 60 s at the furnace temperature <750°C under the direct current electric field of 300 V cm−1. The FS process, microstructure and the electrical performance of ZnO–Bi2O3-based varistors were systematically investigated. Findings The doping of MnO2 significantly decreased the onset temperature of FS and improved the electrical performance of FS ZnO varistor ceramic. The sample with 0.5 mol% MnO2 doping shows the highest improvement, with the nonlinear coefficient of 18, the leakage current of 16.82 µA, the threshold voltage of 459 V/mm and the dielectric constant of 1,221 at 1 kHz. Originality/value FS is a wonderful technology to enhance ZnO varistors for its low energy consumption, and a short sintering time can reduce grain growth and inhabit Bi2O3 volatilize, yet few research studies work on that. In this research, the authors analyzed the FS process and improved the electrical characteristics through MnO2 doping.

The purpose of this study is to explore the teaching methods and related theoretical studies of gender differences in bel canto. Focusing on four aspects: breathing, vocalization, resonance, and emotional expression, this study implements vocal music through gender-differentiated teaching methods and strategies. By carrying out a case study, the author summarizes the application and effectiveness of these teaching methods in the teaching of bel canto, and draws the following conclusions based on the research results: first, teaching methods tailored for gender differences enable students to make rapid progress in singing, breathing, vocalization, resonance, and emotional expression; their goals of learning vocal music are clearer. Second, the gender- dependent teaching methods promote the amelioration of vocal music teaching, break through the difficulties in practical teaching, and improve the teaching level and ability of instructors. Finally, this article puts forward teaching and research suggestions for vocal teachers and vocal education.